Methods and compositions for modification of the HPRT locus

ABSTRACT

Nucleases and methods of using these nucleases for modification of an HPRT locus and for increasing the frequency of gene modification at a targeted locus and clones and for generating animals.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the following U.S. ProvisionalPatent application No. Appl. No. 61/552,309, filed Oct. 27, 2011 andU.S. Prov. Appl. No. 61/556,691, filed Nov. 7, 2011; the disclosures ofwhich are incorporated by reference in their entireties for allpurposes.

TECHNICAL FIELD

The present disclosure is in the fields of genome editing.

BACKGROUND

Gene therapy holds enormous potential for a new era of humantherapeutics. These methodologies will allow treatment for conditionsthat heretofore have not been addressable by standard medical practice.Gene therapy can include the many variations of genome editingtechniques such as disruption or correction of a gene locus, andinsertion of an expressible transgene that can be controlled either by aspecific exogenous promoter fused to the transgene, or by the endogenouspromoter found at the site of insertion into the genome.

Delivery and insertion of the transgene are examples of hurdles thatmust be solved to implement this technology. For example, although avariety of gene delivery methods are potentially available fortherapeutic use, all involve substantial tradeoffs between safety,durability and level of expression. Methods that provide the transgeneas an episome (e.g. basic adenovirus, AAV and plasmid-based systems) aregenerally safe and can yield high initial expression levels, howeverthese methods lack robust episome replication which may limit theduration of expression in mitotically active tissues or those thatregenerate over time. In contrast, delivery methods that result in therandom integration of the desired transgene (e.g. integratinglentivirus) provide more durable expression but might provokeunregulated growth in the recipient cells, potentially leading tomalignancy via activation of oncogenes in the vicinity of the randomlyintegrated transgene cassette. Moreover, although transgene integrationavoids replication-driven loss, it does not prevent eventual silencingof the exogenous promoter fused to the transgene. Over time, suchsilencing results in reduced transgene expression for the majority ofrandom insertion events. Integration of a transgene rarely occurs inevery target cell, which can make it difficult to attain a high enoughlevel of transgene expression to achieve the desired therapeutic effect.

In recent years, a new strategy for transgene integration has beendeveloped that uses cleavage with site-specific nucleases to biasinsertion into a chosen genomic locus (see, e.g. co-owned U.S. Pat. No.7,888,121 and U.S. Patent Publication No. 20110301073). This approachoffers the prospect of improved transgene expression, increased safetyand expressional durability, as compared to classic integrationapproaches, since it allows exact transgene positioning at a minimalrisk of gene silencing or activation of nearby oncogenes.

One approach involves the integration of a transgene into its cognatelocus, for example, insertion of a wild type factor VIII transgene intothe endogenous factor VIII locus to correct a mutant gene.Alternatively, the transgene may be inserted into a non-cognate locuschosen specifically for its beneficial properties. Targeting the cognatelocus can be useful if one wishes to replace expression of theendogenous gene with the transgene while still maintaining theexpressional control exerted by the endogenous regulatory elements.Specific nucleases can be used that cleave within or near the endogenouslocus and the transgene can be integrated at or near the site ofcleavage through homology directed repair (HDR) or by end capture duringnon-homologous end joining (NHEJ). The integration process is influencedby the use or non-use of regions of homology on the transgene donors.These regions of chromosomal homology on the donor flank the transgenecassette and are homologous to the sequence of the endogenous locus atthe site of cleavage.

Alternatively, the transgene may be inserted into a specific “safeharbor” location in the genome that may either utilize the promoterfound at that safe harbor locus, or allow the expressional regulation ofthe transgene by an exogenous promoter that is fused to the transgeneprior to insertion. Several such “safe harbor” loci have been described,including the AAVS1 (also known as PPP1R12C) and CCR5 genes in humancells, Rosa26 and albumin (see co-owned U.S. Patent Publication Nos.20080299580, 20080159996 and 201000218264 and U.S. application Ser. Nos.13/624,193 and 13/624,217). As described above, nucleases specific forthe safe harbor can be utilized such that the transgene construct isinserted by either HDR- or NHEJ-driven processes.

6-thioguanine (6-TG) is a guanine analog that can interfere with dGTPbiosynthesis in the cell. Thio-dG can be incorporated into DNA duringreplication in place of guanine, and when incorporated, often becomesmethylated. This methylation can interfere with proper mis-match DNArepair and can result in cell cycle arrest, and/or initiate apoptosis.6-TG has been used clinically to treat patients with certain types ofmalignancies due to its toxicity to rapidly dividing cells.

Treatment of some types of medical conditions, such as cancers,autoimmune diseases and the like often involves an immunoablation toremove the patient's own immune system, for example, prior to transplantof a bone marrow or other tissue graft. Immunoablation can beaccomplished by total body radiation or by high dose chemotherapy.Although such treatment is thought to “reboot” the immune system byallowing the graft to take hold in the patient, the immunoablationtreatment is often harsh and not well tolerated by the patient and canlead to severe complications depending on the treatment regime utilized.Thus, there is a need for a milder regiment for immunoablative therapy.

Hypoxanthine-guanine phosphoribosyltransferase (HPRT) is an enzymeinvolved in purine metabolism encoded by the HPRT1 gene. HPRT1 islocated on the X chromosome, and thus is present in single copy inmales. HPRT1 encodes the transferase that catalyzes the conversion ofhypoxanthine to inosine monophosphate and guanine to guanosinemonophosphate by transferring the 5-phosphorobosyl group from5-phosphoribosyl 1-pyrophosphate to the purine. The enzyme functionsprimarily to salvage purines from degraded DNA for use in renewed purinesynthesis. In the presence of 6-TG, HPRT is the enzyme responsible forthe integration of 6-TG into DNA and RNA in the cell, resulting inblockage of proper polynucleotide synthesis and metabolism. Thus, 6-TGcan be used as a selection agent to kill cells with a functional HPRTenzyme, and in addition, 6-TG can be given to cause mild immunoablationin subjects in need thereof. In a patient receiving a stem cell graft(e.g. hematopoietic or progenitor stem cells), a transgene of interestcan be integrated into the HPRT locus, knocking out the HPRT1 gene. Sucha cell population will be resistant to 6-TG toxicity. Thus when thetransgene(+)/HPRT1(−) cells are infused into the patient, a mild courseof 6-TG may increase engraftment of the cells, and those cells thatengraft will have a greater percentage of transgene integration.

HPRT has been targeted traditionally as a safe harbor for transgeneintegration (see for example Jasin et al (1996) Proc Natl Acad Sci USA93, p. 8804). It is constitutively expressed at a low level, anddisruption of the HPRT gene can be selected for both in vitro and invivo using 6-TG. However, integration into an HPRT locus via randomintegration can be difficult and occurs only at a low frequency.

Thus, there remains a need for compositions and methods to increase thefrequency of specific genome editing by directly targeting the HPRTgene, or by using targeted disruption of this gene as a marker both forthe successful transduction of nucleic acids into a cell (at the HPRT orother loci) and as a marker for expression and function of thetransfected nuclease(s).

SUMMARY

Disclosed herein are methods and compositions for increasing targetedinsertion of a transgene into a specific location within the cell orincreasing the frequency of gene modification in a targeted locus. Insome embodiments, transgene insertion occurs at the HPRT gene, andselection of transgene insertion occurs by using exposure of the cell,animal, or patient to 6-TG. In other embodiments, disruption of the HPRTgene by nuclease cleavage (e.g., gene knockout due to nucleotideinsertion or deletion during NHEJ following cleavage) serves as a proxyfor cells with active nuclease activity, and transgene insertion occursat one or more other locations within the genome in the presence of anadditional nuclease co-transduced with the donor transgene and theHPRT-specific nuclease. Insertion can occur at any locus, including, forexample, a safe harbor location, such as AAVS1, Rosa, Albumin or CCR5,or at the endogenous location of any gene of interest. Insertion of atransgene into a corresponding endogenous locus can be for gene knockout, gene correction, or for the introduction of gene variants withdesired attributes or for the introduction of a gene encoding apolypeptide or polynucleotide of interest.

In some embodiments, two or more sets of nucleases, where one settargets HPRT and the other targets another location of interest, areintroduced (simultaneously and/or sequentially in any order) into thecell, such that knock out of both loci occurs through NHEJ-mediatedrepair of the double strand breaks (DSB) induced by cleavage by thenuclease sets. In these embodiments, nuclease-mediated HPRT disruptionis used as a marker for successful transduction of the nuclease pairs,as well as for an indicator of cells containing nuclease activity. Thisis useful for increasing the efficiency of identification of cells inwhich genome editing has likely occurred. In some embodiments, themethods and compositions are used in T or B cells, and in others, theyare used in stem cells, for example hematopoietic stem cells (e.g.,CD34+ cells). In some embodiments, the methods and compositions of theinvention are used with hematopoietic stem/progenitor cells.

In one aspect, described herein is a zinc-finger protein (ZFP) thatbinds to target site in an HPRT gene in a genome, wherein the ZFPcomprises one or more engineered zinc-finger binding domains. In oneembodiment, ZFPs are used as a pair of zinc-finger nucleases (ZFNs) thatdimerize and then cleave a target genomic region of interest, whereinthe ZFNs comprise one or more engineered zinc-finger binding domains anda nuclease cleavage domain or cleavage half-domain. In another aspect,described herein is a TALE protein (Transcription activator likeeffector) that binds to target site in an HPRT gene in a genome, whereinthe TALE comprises one or more engineered TALE DNA binding domains. Inone embodiment, the TALE is a nuclease (TALEN) that cleaves a targetgenomic region of interest, wherein the TALEN comprises one or moreengineered TALE DNA binding domains and a nuclease cleavage domain orcleavage half-domain Cleavage domains and cleavage half domains of ZFNsand/or TALENs can be obtained, for example, from various restrictionendonucleases and/or homing endonucleases. In one embodiment, thecleavage half-domains are derived from a Type IIS restrictionendonuclease (e.g., Fok I). In certain embodiments, the zinc finger orTALE DNA binding domain recognizes a target site in an HPRT gene, forexample as shown in Tables 1 and 4.

The ZFN or TALEN may bind to and/or cleave an HPRT gene within thecoding region of the gene or in a non-coding sequence within or adjacentto the gene, such as, for example, a leader sequence, trailer sequenceor intron, or within a non-transcribed region, either upstream ordownstream of the coding region.

In another aspect, described herein are compositions comprising one ormore of the zinc-finger or TALE nucleases described herein. In certainembodiments, the composition comprises one or more zinc-finger or TALEnucleases in combination with a pharmaceutically acceptable excipient.In some embodiments, the composition comprises two or more sets of zincfinger or TALE nucleases, each set with different specificities. In someaspects, one set of the zinc-finger or TALE nucleases is specific for anHPRT gene. In other aspects, the composition comprises both ZFNs andTALENs. In some embodiments, the composition comprises polynucleotidesencoding HPRT-specific nucleases, while in other embodiments, thecomposition comprises nuclease proteins.

In another aspect, described herein is a polynucleotide encoding one ormore ZFNs or TALENs described herein. The polynucleotide may be, forexample, mRNA or DNA. In some aspects, the mRNA may be chemicallymodified (See e.g. Kormann et al, (2011) Nature Biotechnology29(2):154-157). In another aspect, described herein is a ZFN or TALENexpression vector comprising a polynucleotide, encoding one or more ZFNsor TALENs described herein, operably linked to a promoter. In oneembodiment, the expression vector is a viral vector. In one aspect, theviral vector exhibits tissue specific tropism.

In another aspect, described herein is a host cell comprising one ormore ZFN or TALEN expression vectors. The host cell may be stablytransformed or transiently transfected or a combination thereof with oneor more ZFN or TALEN expression vectors. In one embodiment, the hostcell is an embryonic stem cell. In other embodiments, the one or moreZFN or TALEN expression vectors express one or more ZFNs or TALENs inthe host cell. In another embodiment, the host cell may further comprisean exogenous polynucleotide donor sequence. In any of the embodiments,described herein, the host cell can comprise an embryo cell, for examplea one or more mouse, rat, rabbit or other mammal cell embryo (e.g., anon-human primate). In some embodiments, the host cell comprises atissue.

In another aspect, described herein is a method for cleaving an HPRTgene in a cell, the method comprising: (a) introducing, into the cell,one or more polynucleotides encoding one or more ZFNs or TALENs thatbind to a target site in the one or more genes under conditions suchthat the ZFN(s) is (are) or TALENs is (are) expressed and the one ormore HPRT genes are cleaved. Co-transduction of both sets is performedand then the recipient cells can be selected using 6-TG. In otherembodiments, cells resistant to 6-TG through a knockout of HPRT by NHEJfollowing the nuclease-induced DSB can also be modified vianuclease-mediated cleavage at a different (non-HPRT) site, for examplevia cleavage by the second nuclease set followed by NHEJ. Examples ofgenes that may be knocked out by this protocol include the HIVco-receptors CCR5 or CXCR4.

In other embodiments, a genomic sequence in the target gene is cleaved,for example using a ZFN or TALEN (or vector encoding said ZFN or TALEN)as described herein and a “donor” sequence inserted into the genefollowing targeted cleavage with the ZFN or TALEN. The donor sequencemay be present in the ZFN or TALEN vector, present in a separate vector(e.g., Ad, AAV or LV vector) or, alternatively, may be introduced intothe cell using a separate and/or different nucleic acid deliverymechanism. Insertion of a donor nucleotide sequence into the HPRT locuscan result in the expression of the transgene under control of the HPRTgenetic control elements. In some aspects, insertion of the transgene ofinterest results in expression of an intact exogenous protein sequenceand lacks any HPRT-encoded amino acids. In other aspects, the expressedexogenous protein is a fusion protein and comprises amino acids encodedby the transgene and by the HPRT gene. In some instances, the HPRTsequences will be present on the amino (N)-terminal portion of theexogenous protein, while in others, the HPRT sequences will be presenton the carboxy (C)-terminal portion of the exogenous protein. In otherinstances, HPRT sequences will be present on both the N- and C-terminalportions of the exogenous protein.

In some embodiments, the invention describes methods and compositionsthat can be used to express a transgene under the control of the HPRTpromoter in vivo. In some aspects, the transgene may encode atherapeutic protein of interest. The transgene may encode a protein suchthat the methods of the invention can be used for protein replacement.In some aspects, the transgenes are inserted into B cells for productionof the protein encoded by the transgene for export into the blood. Othernon-limiting examples include treatment of hemoglobinopathies in CD34+stem/progenitor cells by introduction of wild-type or anti-sicklingglobin sequences in patients with aberrant globin genes. In someaspects, the transgenes encode therapeutic proteins, therapeutichormones, plasma proteins, antibodies and the like. Another non-limitingexample includes the insertion of a chimeric antigen receptor (CAR) orinsertion of one or more T cell receptor gene(s) into a T cell ex vivofor reinfusion into a patient in need thereof (See Jena et al (2010)Blood 116:1035-1044). In further aspects, the methods and compositionsof the invention are used to knock out a gene in a cell. A non-limitingexample includes the knock out of a viral receptor such as CCR5 in Tcells ex vivo for reinfusion into a patient in need thereof. Treatmentof hemoglobinopathy by knockout of the Bcl11A gene or EKLF gene, or byknocking out the EKLF binding site in the Bcl11A gene, all which willresult in a reactivation of fetal (γ) globin synthesis, are othernon-limiting examples. Other embodiments include the knockout of HLAgenes or gene correction of a gene or insertion of splice acceptorsites.

In some embodiments, the ZFN or TALEN cleavage site is in an intron ofthe HPRT gene such that repair of the ZFN- or TALEN-induced DSB usingNHEJ will produce a cell that remains sensitive to 6-TG. In someembodiments, the DNA integrated into HPRT contains a splice acceptorsequence to disrupt normal splicing of HPRT wherein disruption of HPRTsplicing inactivates the gene, creating 6-TG resistant cells. In someembodiments, the integrated DNA contains a transgene that uses thecaptured splice-form to produce a fusion protein with HPRT. In otherembodiments, the integrated DNA comprises a promoter and a transgenesuch that HPRT splicing is disrupted and the transgene is expressed.

In other embodiments, disruption of the HPRT gene by nuclease cleavage,(e.g., gene knockout due to nucleotide insertion or deletion duringNHEJ) serves as a marker for positive transduction and active nucleaseactivity, and transgene insertion can occur at another location withinthe genome (e.g. a safe harbor). Such methods of enriching fornuclease-modified cells and compositions can be used to enrich formodifications at a locus other than HPRT, for example inactivation ofand/or integration of a transgene at a non-HPRT locus. The transgene maybe under the control of another endogenous or exogenous promoter ofinterest in vivo or in vitro. In some aspects, the transgene may encodea protein of interest, for example a therapeutic or replacement protein(e.g., hormones, plasma proteins, antibodies, etc.) Non-limitingexamples of transgenes encoding protein therapeutics or replacementsinclude sequences encoding wild type globin proteins (e.g., in CD34+stem cells for the treatment of hemoglobinopathies in patients withaberrant globin genes); a chimeric antigen receptor (CAR) and/or T-cellreceptor gene(s) (e.g., ex vivo insertion in a T cell for reinfusioninto a patient in need thereof); clotting factors (e.g., for thetreatment of subjects with clotting disorders, for example via ex vivoor in vivo targeted insertion hematopoietic cells or CD34+ hematopoieticstem cells, hepatocytes or hepatic stem cells); and/or one or moreanti-HIV proteins, and insertion of wild type copies of aberrant genesfor correction or prevention of a disease (e.g. treatment of a lysosomalstorage disease).

In further aspects, the methods and compositions of the invention areused to monitor knock out of a gene in a cell. A non-limiting exampleincludes monitoring the nuclease-mediated knock out of a viral receptorsuch as CCR5 in T cells ex vivo for reinfusion into a patient in needthereof. Other embodiments include gene correction of a gene orinsertion of splice acceptor sites. In these embodiments, the HPRT knockout as described herein, followed by exposure of the cells to 6-TG invivo or in vitro selects cells in which transduction of thenuclease-mediated targeted modification (e.g., inactivation orinsertion) at a locus other than HPRT has been successful due tonuclease activity.

In some embodiments, the methods of the invention may be used in vivo inthe development of transgenic animal systems. In some aspects, thetransgenic animal may be used in model development where the transgeneencodes a human gene. In some instances, the transgenic animal may beknocked out at the corresponding endogenous locus, allowing thedevelopment of an in vivo system where the human protein may be studiedin isolation. Such transgenic models may be used for screening purposesto identify small molecules, large biomolecules or other entities whichmay interact or modify the human protein of interest. In other aspects,the transgenic animals may be used for production purposes, for example,to produce antibodies or other biomolecules of interest. In certainembodiments, the animal is a small mammal, for example a rabbit or arodent such as rat, a mouse or a guinea pig. In other embodiments, theanimal is a non-human primate. In yet further embodiments, the animal isa farm animal such as a cow, goat or pig. In some aspects, the transgeneis integrated into the HPRT locus in an embryonic stem cell or animalembryo by any of the methods described herein, and then the embryo isimplanted such that a live animal is born. The animal is then raised tosexual maturity and allowed to produce offspring wherein at least someof the offspring comprise the integrated transgene.

In a still further aspect, provided herein is a method for site specificintegration of a nucleic acid sequence into an HPRT locus of achromosome. In certain embodiments, the method comprises: (a) injectingan embryo with (i) at least one DNA vector, wherein the DNA vectorcomprises an upstream sequence and a downstream sequence flanking thenucleic acid sequence to be integrated, and (ii) at least one RNAmolecule encoding a zinc finger or TALE nuclease that recognizes thesite of integration in the HPRT locus, and (b) culturing the embryo toallow expression of the zinc finger or TALE nuclease, wherein a doublestranded break introduced into the site of integration by the zincfinger nuclease or TALEN is repaired, via homologous recombination withthe DNA vector, so as to integrate the nucleic acid sequence into thechromosome.

Suitable embryos may be derived from several different vertebratespecies, including mammalian, bird, reptile, amphibian, and fishspecies. Generally speaking, a suitable embryo is an embryo that may becollected, injected, and cultured to allow the expression of a zincfinger or TALE nuclease. In some embodiments, suitable embryos mayinclude embryos from small mammals (e.g., rodents, rabbits, etc.),companion animals, livestock, and primates. Non-limiting examples ofrodents may include mice, rats, hamsters, gerbils, and guinea pigs.Non-limiting examples of companion animals may include cats, dogs,rabbits, hedgehogs, and ferrets. Non-limiting examples of livestock mayinclude horses, goats, sheep, swine, llamas, alpacas, and cattle.Non-limiting examples of primates may include capuchin monkeys,chimpanzees, lemurs, macaques, marmosets, tamarins, spider monkeys,squirrel monkeys, and vervet monkeys. In other embodiments, suitableembryos may include embryos from fish, reptiles, amphibians, or birds.Alternatively, suitable embryos may be insect embryos, for instance, aDrosophila embryo or a mosquito embryo.

In any of the methods or compositions described herein, the cellcontaining the engineered HPRT locus or other genomic editing can be astem or progenitor cell. Specific stem cell types that may be used withthe methods and compositions of the invention include embryonic stemcells (ESC), induced pluripotent stem cells (iPSC) and hematopoieticstem cells (e.g., CD34+ cells). The iPSCs can be derived from patientsamples and from normal controls wherein the patient derived iPSC can bemutated to the normal or wild type gene sequence at the gene ofinterest, or normal cells can be altered to the known disease allele atthe gene of interest. Similarly, the hematopoietic stem cells can beisolated from a patient or from a donor. These cells are then engineeredto express the transgene or gene modification of interest, expanded andthen reintroduced into the patient.

In any of the methods described herein, the polynucleotide encoding thezinc finger nuclease(s) or TALEN(s) can comprise DNA, RNA orcombinations thereof. In certain embodiments, the polynucleotidecomprises a plasmid. In other embodiments, the polynucleotide encodingthe nuclease comprises mRNA.

Also provided is an embryo comprising at least one DNA vector, whereinthe DNA vector comprises an upstream sequence and a downstream sequenceflanking the nucleic acid sequence to be integrated, and at least oneRNA molecule encoding a zinc finger nuclease that recognizes thechromosomal site of integration. Organisms derived from any of theembryos as described herein are also provided.

In another aspect, the methods and compositions of the invention providefor the use of cells, cell lines and animals (e.g., transgenic animals)in the screening of drug libraries and/or other therapeutic compositions(i.e., antibodies, structural RNAs, etc.) for use in treatment of ahemoglobinopathy, lysosomal storage disease, musculoskeletal disease, aclotting disorder, cancer, HIV or the like. Such screens can begin atthe cellular level with manipulated cell lines or primary cells, and canprogress up to the level of treatment of a whole animal (e.g., human).

A kit, comprising the ZFPs or TALENs of the invention, is also provided.The kit may comprise nucleic acids encoding the ZFPs or TALENs, (e.g.RNA molecules or ZFP or TALEN encoding genes contained in a suitableexpression vector), donor molecules, suitable host cell lines,instructions for performing the methods of the invention, and the like.

These and other aspects will be readily apparent to the skilled artisanin light of the disclosure as a whole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, panels A and B, depict gels demonstrating the results of a Cel-Imismatch assay (Surveyor™, Transgenomic) that measures cleavage at alocation of interest by a set of zinc finger nuclease pairs that hasbeen followed by an NHEJ event. NHEJ causes the insertion or deletion ofnucleotide bases (“indels”) which then creates a mismatch when the DNAstrand is annealed with a wild type DNA strand. The Cel-I enzyme thencleaves the DNA at the site of this mismatch, creating two smallerfragments. The figure shows results after transfection of HPRT zincfinger nuclease pairs into K562 cells (FIG. 1A) or murine Neuro2A cells(FIG. 1B). The percent mismatch, or “% NHEJ”, corresponds to thepercentage of modified alleles and is a measure of the nuclease activityof each pair, and is indicated at the bottom of each lane. GFP arecontrol cells that have been transfected with a GFP encoding plasmid.

FIG. 2 depicts a gel measuring the percent of indels in cells that weretransfected with HPRT specific ZFNs and then treated with 6-TG. The K562cells were also transfected with ZFN pairs specific for either CCR5 orthe glucocorticoid receptor locus (GR). Cel-I experiments (as describedabove) were performed on cells at the HPRT locus after 10 to 14 days ofgrowth in 6-TG. HPRT resistant cells were only observed in those samplesthat had been treated with the ZFNs targeting the HPRT locus. The lanesare numbered 1 to 13 at the top and show the following: Lanes 1-3 showCel-I results using 80 ng HPRT-specific ZFN and 400 ng CCR5-specificZFNs (see, e.g., U.S. Pat. No. 7,951,925) 3 days after ZFNadministration (lane 1) in the absence (lane 2) or presence (lane 3) of6-TG. Lanes 4-6 show Cel-I results using 20 ng HPRT-specific ZFN and 80ng CCR5-specific ZFNs (see, e.g., U.S. Pat. No. 7,951,925) 3 days afterZFN administration (lane 4) in the absence (lane 5) or presence (lane 6)of 6-TG. Lanes 7-9 show Cel-I results using 80 ng HPRT-specific ZFN and400 ng GR-specific ZFNs (see, e.g., U.S. Patent Publication No.20080188000) 3 days after ZFN administration (lane 7) in the absence(lane 8) or presence (lane 9) of 6-TG. Lanes 10-13 show Cel-I resultsusing 20 ng HPRT-specific ZFN and 80 ng GR-specific ZFNs (see, e.g.,U.S. Patent Publication No. 20080188000) 3 days after ZFN administration(lane 10) in the absence (lane 11) or presence (lane 12) of 6-TG or GFP(lane 13).

FIG. 3 depicts a gel measuring the percent of indels in K562 cells thatwere transfected with HPRT specific ZFNs as well as with another pair ofZFNs targeting the CCR5 locus. The cells were then selected on 6-TG. DNAwas isolated from the cells following the selection, and the Cel-I assaywas performed at the CCR5 locus. As can be seen, selection of thetransfected cells on 6-TG enriches cells that had been cleaved at CCR5.Lanes are as follows: Sample number lane (1, 2, etc.) depicts theresults of the Cel-I assay performed on DNA harvested three daysfollowing transfection. Numbers or (−) above the boxed gel indicate thengs of DNA used in transfection reaction. “*” indicates the use of anuclease pair with the engineered, obligate heterodimeric ELD/KKR FokIdomains while “*” indicates that the nuclease pair includes the DD/RRFokI obligate heterodimer domains. See, U.S. Patent Publication No.20110201055. In the sample section, (−) or (+) indicates DNA isolatedfrom cells grown either in the absence or presence of 6-TG,respectively. Percent of modification observed is indicated at thebottom of each lane.

FIG. 4 depicts a gel measuring the percent cutting at a restriction siteintroduced into the HPRT locus. The K562 cells were transfected withvectors comprising the HPRT-specific ZFNs. Donor molecules were alsoincluded comprising the novel restriction site and either a shorter (359nucleotides) or a longer (725 nucleotides) region of homology with theHPRT locus flanking the insertion site (“arms”). All donors wereintroduced using a plasmid based approach, but in one set ofexperiments, the donor plasmid additionally carried an enhancer element(“short arm+ en”). All conditions were successful in introducing thedonor carrying the restriction site into the HPRT locus which wasenriched up to 3-fold and up to levels exceeding 40% of the alleles when6-TG selection was used.

FIG. 5, panels A and B, depict the integration of a GFP transgene intothe HPRT locus in K562 cells. FIG. 5A demonstrates that the transgenewas integrated via homologous recombination of the donor which wasenriched 2-3 fold by 6-TG selection as measured in a semi-quantitativePCR based assay. FIG. 5B depicts an illustration showing the location ofthe 3 PCR primers used for the amplification in the assay, showing thatthe integration causes a larger PCR product to be produced (indicated byarrow in 5A) from the pgkr1+15512f primer pair while the HPRTr1-16078+15512f primer pair generates a shorter band from the unmodifiedlocus. The use of the common forward primer 15512f and the generation ofboth wild type and integration specific bands allowed the PCR reactionto be used as a semi-quantitative assessment of the efficiency oftargeted integration.

FIG. 6 is a gel depicting the results of a restriction enzyme digestionfollowing targeted integration of a donor containing a HhaI restrictionsite into the β-globin locus. In this experiment, the donor was insertedinto the β-globin locus in K562 cells following co-transfection of ZFNsspecific for HPRT, ZFNs specific for beta-globin and the beta-globinspecific donor. After recovery from transfection, the cells were splitand one group was selected with 6-TG. DNA was isolated from the cellsand the β-globin locus was PCR amplified, and then subject torestriction digestion with HhaI. A dramatic increase in the frequency ofHha I specific fragments related to successful gene insertion (indicatedby arrows) at the beta globin locus was observed following the 6-TGselection.

FIG. 7 is a gel depicting modification of the HPRT locus in mobilizedhuman CD34+ stem cells. HPRT specific ZFN expression plasmids weretransfected into CD34+ cells and after recovery from the nucleofection,they were split and selected on 6-TG. Modification of the HPRT locus wasanalyzed by the Cel-I assay as described above and the percent of indelsis shown at the bottom of each lane. 6-TG selection increased thepercentage of HPRT modified genomes in the cell pool.

FIG. 8, panels A and B, depict modification of the HPRT locus in K562cells using HPRT-specific TALENs. FIG. 8A depicts results of a Cel-Iassay where the HPRT locus from nuclease treated cells was PCR amplifiedand then subjected to the Cel-I assay. Triangles over the sets indicateincreasing amounts of TALEN expression plasmids used in thetransfection. FIG. 8B depicts the amount of genome modification (%indels) as determined by the Cel-I assay.

FIG. 9 is an alignment of the DNA sequences in the canine and human HPRTlocus corresponding to the target region cleaved by the ZFN and TALENnucleases. The canine (“dog”) DNA sequence is shown on the top of eachpair of sequences (SEQ ID NOs:61, 63, 65 and 67, as indicated in theFigure) and the human DNA sequence is shown below (SEQ ID NOs:62, 64, 66and 68, as indicated in the Figure). Text in the sequences that is ingrey highlight indicates nucleotides that are not homologous between thetwo DNA sequences. Black boxes under the aligned DNA sequences indicatethe TALEN binding sites while grey outlined boxes indicate the ZFNbinding sites. Arrows indicate which DNA strand the nucleases bind towith the left-to-right arrows indicating a binding site on the 5′-3′ orWatson strand and a right-to-left arrow indicating a binding site on the3′-to-5′ or Crick strand.

FIG. 10 depicts a gel showing the results of a Cel-I mismatch assay onDNA isolated from the canine cell line D17 that had been transfectedwith various human HPRT-specific nuclease pairs (individual lanes areidentified in Table 6 below). The percent of modification detected (“%NHEJ”) is shown at the bottom of each lane.

FIG. 11 depicts a gel showing the results of a Cel-I mismatch assay onDNA isolated from the rhesus monkey cell line LLC-MK2 that had beentransfected with various human HPRT-specific nuclease pairs. The percentof modification detected (“% NHEJ”) is shown at the bottom of each lane.

FIG. 12 depicts a series of gels showing the results of a Cel-I mismatchassay on DNA isolated from human CD34+ cells that had been transfectedindividually with six human HPRT-specific nuclease pairs, each of whichcleaves in an intron. “Site” refers to the target site that each ZFNpair cleaves. In addition, an additional ZFN pair (“A′”) was tested inK562 cells. The percent of modification detected (“% NHEJ”) is shown atthe bottom of each lane.

FIG. 13, panels A to F, depict gels showing the targeted integration inCD34+ cells of an oligo donor into each of the six loci cleaved in FIG.12. The percent of targeted modification detected is shown at the bottomof each lane.

FIG. 14, panels A-C, depict the integration of a SA-2A-GFP-pA transgeneinto the HPRT locus in human K562 cells. FIG. 14A shows a schematic ofthe integrated transgene and illustrates where sequence will be deletedupon splicing. FIG. 14B depicts the percent of cells containing the GFPtransgene in each of the conditions tested, with (right bars) andwithout (left bars) 6-TG selection. FIG. 14C is a graph showing cellviability in each of the conditions (left bars show with no selectionand right bars shows with 6-TG selection.

FIG. 15, panels A and B, depict PCR detection of targeted integration ofthe SA-2A-GFP-pA cassette into HPRT in human K562 cells without 6-TGselection. FIG. 15A is a schematic of the integrated transgene andincludes the location of the PCR primers used for amplification. FIG.15B depicts a gel showing the PCR products and demonstrates targetedintegration of the GFP transgene through targeted insertion (GFP TI) inthe absence of selection.

FIG. 16 is a graph depicting integration of the SA-2A-GFP-pA transgeneinto the HPRT intronic locus in human CD34+ cells. The left-most barshows the percentage of GFP-positive cells.

DETAILED DESCRIPTION

Disclosed herein are methods and compositions for increasing insertionof a transgene into a specific location within the cell or increasingthe frequency of gene editing or modification of a targeted locus. Insome embodiments, the genome editing involves insertion of an exogenoustransgene at an HPRT locus (e.g., HPTR1), and selection of transgeneinsertion occurs by exposure of the cell or animal to 6-TG. In otherembodiments, disruption of an HPRT gene by nuclease cleavage (e.g.,cleavage followed by gene knockout due to nucleotide insertion ordeletion during NHEJ) serves as a marker for active nuclease activity,for example transgene insertion, at one or more other (non-HPRT) loci,In other embodiments, introduction of a nuclease pair targeting HPRT anda separate nuclease pair targeting a separate locus of interest resultsin gene knockout in both locations by NHEJ mediated double strand breakrepair.

Thus, the methods and compositions of the invention can be used toincrease the efficiency of genome editing in a desired setting throughthe use of HPRT knockout, either by gene knock out, or by targetedinsertion of a transgene into HPRT, followed in either instance by 6-TGselection. For example, the compositions and methods described hereincan be used to insert a transgene that encodes and/or expresses atherapeutically beneficial protein (e.g., proteins such as globins orother involved in blood disorders such as clotting, anti-HIV proteins,CARs, T-cell receptor genes and a variety of other proteins, includingmonogenic proteins). Alternatively, these methods can be used toknockout another gene for therapeutic benefit or otherwise (e.g.,knocking out of a repressor is beneficial if the gene product from therepressor gene is suppressing a gene whose product is needed).

Any of the compositions and methods described herein can be used forgene knock out and/or transgene insertion in any host cell. In certainembodiments, the cells are patient derived cells, e.g. patient derivedinduced pluripotent stem cells (iPSCs) or other types of stems orprogenitor cells (embryonic, hematopoietic, neural, or mesenchymal as anon-limiting set). These altered stem cells can be hematopoietic orprogenitor stem cells, for example, which can then be used in a bonemarrow transplant. Alternatively, gene knock out and/or transgeneintegration can be accomplished in patient derived cells such as T cellsex vivo wherein the modified cells can then be reintroduced into thepatient. Non-limiting examples of desirable loci for modificationinclude viral receptors such as CD4, CCR5 or CXCR4.

General

Practice of the methods, as well as preparation and use of thecompositions disclosed herein employ, unless otherwise indicated,conventional techniques in molecular biology, biochemistry, chromatinstructure and analysis, computational chemistry, cell culture,recombinant DNA and related fields as are within the skill of the art.These techniques are fully explained in the literature. See, forexample, Sambrook et al. MOLECULAR CLONING: A LABORATORY MANUAL, Secondedition, Cold Spring Harbor Laboratory Press, 1989 and Third edition,2001; Ausubel et al., CURRENT PROTOCOLS IN MOLECULAR BIOLOGY, John Wiley& Sons, New York, 1987 and periodic updates; the series METHODS INENZYMOLOGY, Academic Press, San Diego; Wolffe, CHROMATIN STRUCTURE ANDFUNCTION, Third edition, Academic Press, San Diego, 1998; METHODS INENZYMOLOGY, Vol. 304, “Chromatin” (P. M. Wassarman and A. P. Wolffe,eds.), Academic Press, San Diego, 1999; and METHODS IN MOLECULARBIOLOGY, Vol. 119, “Chromatin Protocols” (P. B. Becker, ed.) HumanaPress, Totowa, 1999.

DEFINITIONS

The terms “nucleic acid,” “polynucleotide,” and “oligonucleotide” areused interchangeably and refer to a deoxyribonucleotide orribonucleotide polymer, in linear or circular conformation, and ineither single- or double-stranded form. For the purposes of the presentdisclosure, these terms are not to be construed as limiting with respectto the length of a polymer. The terms can encompass known analogues ofnatural nucleotides, as well as nucleotides that are modified in thebase, sugar and/or phosphate moieties (e.g., phosphorothioatebackbones). In general, an analogue of a particular nucleotide has thesame base-pairing specificity; i.e., an analogue of A will base-pairwith T.

The terms “polypeptide,” “peptide” and “protein” are usedinterchangeably to refer to a polymer of amino acid residues. The termalso applies to amino acid polymers in which one or more amino acids arechemical analogues or modified derivatives of correspondingnaturally-occurring amino acids.

“Binding” refers to a sequence-specific, non-covalent interactionbetween macromolecules (e.g., between a protein and a nucleic acid). Notall components of a binding interaction need be sequence-specific (e.g.,contacts with phosphate residues in a DNA backbone), as long as theinteraction as a whole is sequence-specific. Such interactions aregenerally characterized by a dissociation constant (K_(d)) of 10⁻⁶ M⁻¹or lower. “Affinity” refers to the strength of binding: increasedbinding affinity being correlated with a lower K_(d).

A “binding protein” is a protein that is able to bind non-covalently toanother molecule. A binding protein can bind to, for example, a DNAmolecule (a DNA-binding protein), an RNA molecule (an RNA-bindingprotein) and/or a protein molecule (a protein-binding protein). In thecase of a protein-binding protein, it can bind to itself (to formhomodimers, homotrimers, etc.) and/or it can bind to one or moremolecules of a different protein or proteins. A binding protein can havemore than one type of binding activity. For example, zinc fingerproteins have DNA-binding, RNA-binding and protein-binding activity.

A “zinc finger DNA binding protein” (or binding domain) is a protein, ora domain within a larger protein, that binds DNA in a sequence-specificmanner through one or more zinc fingers, which are regions of amino acidsequence within the binding domain whose structure is stabilized throughcoordination of a zinc ion. The term zinc finger DNA binding protein isoften abbreviated as zinc finger protein or ZFP.

A “TALE DNA binding domain” or “TALE” is a polypeptide comprising one ormore TALE repeat domains/units. The repeat domains are involved inbinding of the TALE to its cognate target DNA sequence. A single “repeatunit” (also referred to as a “repeat”) is typically 33-35 amino acids inlength and exhibits at least some sequence homology with other TALErepeat sequences within a naturally occurring TALE protein. See, also,U.S. Patent Publication No. 20110301073.

Zinc finger binding domains can be “engineered” to bind to apredetermined nucleotide sequence, for example via engineering (alteringone or more amino acids) of the recognition helix region of a naturallyoccurring zinc finger protein. Similarly, TALEs can be “engineered” tobind to a predetermined nucleotide sequence, for example by engineeringof the amino acids involved in DNA binding (the “Repeat VariableDiresidue” or “RVD” region). Therefore, engineered zinc finger proteinsor TALE proteins are proteins that are non-naturally occurring.Non-limiting examples of methods for engineering zinc finger proteinsand TALEs are design and selection. A designed protein is a protein notoccurring in nature whose design/composition results principally fromrational criteria. Rational criteria for design include application ofsubstitution rules and computerized algorithms for processinginformation in a database storing information of existing ZFP or TALEdesigns and binding data. See, for example, U.S. Pat. Nos. 6,140,081;6,453,242; and 6,534,261; see also WO 98/53058; WO 98/53059; WO98/53060; WO 02/016536 and WO 03/016496 and U.S. application Ser. No.13/068,735.

A “selected” zinc finger protein or TALE is a protein not found innature whose production results primarily from an empirical process suchas phage display, interaction trap or hybrid selection. See e.g., U.S.Pat. No. 5,789,538; U.S. Pat. No. 5,925,523; U.S. Pat. No. 6,007,988;U.S. Pat. No. 6,013,453; U.S. Pat. No. 6,200,759; WO 95/19431; WO96/06166; WO 98/53057; WO 98/54311; WO 00/27878; WO 01/60970 WO 01/88197and WO 02/099084 and U.S. patent application Ser. No. 13/068,735.

“Recombination” refers to a process of exchange of genetic informationbetween two polynucleotides. For the purposes of this disclosure,“homologous recombination (HR)” refers to the specialized form of suchexchange that takes place, for example, during repair of double-strandbreaks in cells via homology-directed repair mechanisms. This processrequires nucleotide sequence homology, uses a “donor” molecule totemplate repair of a “target” molecule (i.e., the one that experiencedthe double-strand break), and is variously known as “non-crossover geneconversion” or “short tract gene conversion,” because it leads to thetransfer of genetic information from the donor to the target. Withoutwishing to be bound by any particular theory, such transfer can involvemismatch correction of heteroduplex DNA that forms between the brokentarget and the donor, and/or “synthesis-dependent strand annealing,” inwhich the donor is used to re-synthesize genetic information that willbecome part of the target, and/or related processes. Such specialized HRoften results in an alteration of the sequence of the target moleculesuch that part or all of the sequence of the donor polynucleotide isincorporated into the target polynucleotide.

In the methods of the disclosure, one or more targeted nucleases asdescribed herein create a double-stranded break in the target sequence(e.g., cellular chromatin) at a predetermined site, and a “donor”polynucleotide, having homology to the nucleotide sequence in the regionof the break, can be introduced into the cell. The presence of thedouble-stranded break has been shown to facilitate integration of thedonor sequence. The donor sequence may be physically integrated or,alternatively, the donor polynucleotide is used as a template for repairof the break via homologous recombination, resulting in the introductionof all or part of the nucleotide sequence as in the donor into thecellular chromatin. Thus, a first sequence in cellular chromatin can bealtered and, in certain embodiments, can be converted into a sequencepresent in a donor polynucleotide. Thus, the use of the terms “replace”or “replacement” can be understood to represent replacement of onenucleotide sequence by another, (i.e., replacement of a sequence in theinformational sense), and does not necessarily require physical orchemical replacement of one polynucleotide by another.

In any of the methods described herein, additional pairs of zinc-fingerand/or additional TALEN proteins can be used for additionaldouble-stranded cleavage of additional target sites within the cell.

In certain embodiments of methods for targeted recombination and/orreplacement and/or alteration of a sequence in a region of interest incellular chromatin, a chromosomal sequence is altered by homologousrecombination with an exogenous “donor” nucleotide sequence. Suchhomologous recombination is stimulated by the presence of adouble-stranded break in cellular chromatin, if sequences homologous tothe region of the break are present.

In any of the methods described herein, the first nucleotide sequence(the “donor sequence”) can contain sequences that are homologous, butnot identical, to genomic sequences in the region of interest, therebystimulating homologous recombination to insert a non-identical sequencein the region of interest. Thus, in certain embodiments, portions of thedonor sequence that are homologous to sequences in the region ofinterest exhibit between about 80 to 99% (or any integer therebetween)sequence identity to the genomic sequence that is replaced. In otherembodiments, the homology between the donor and genomic sequence ishigher than 99%, for example if only 1 nucleotide differs as betweendonor and genomic sequences of over 100 contiguous base pairs. Incertain cases, a non-homologous portion of the donor sequence cancontain sequences not present in the region of interest, such that newsequences are introduced into the region of interest. In theseinstances, the non-homologous sequence is generally flanked by sequencesof 50-1,000 base pairs (or any integral value therebetween) or anynumber of base pairs greater than 1,000, that are homologous oridentical to sequences in the region of interest. In other embodiments,the donor sequence is non-homologous to the first sequence, and isinserted into the genome by non-homologous recombination mechanisms.

Any of the methods described herein can be used for partial or completeinactivation of one or more target sequences in a cell by deletion ofsequences and/or by targeted integration of a donor sequence thatdisrupts expression of the gene(s) of interest. Cell lines withpartially or completely inactivated genes are also provided.

Furthermore, the methods of targeted integration as described herein canalso be used to integrate one or more exogenous sequences (also referredto as “donors” or “transgenes”). The exogenous nucleic acid sequence cancomprise, for example, one or more genes or cDNA molecules, or any typeof coding or non-coding sequence, as well as one or more controlelements (e.g., promoters). In addition, the exogenous nucleic acidsequence may produce one or more RNA molecules (e.g., small hairpin RNAs(shRNAs), inhibitory RNAs (RNAis), microRNAs (miRNAs), etc.).

“Cleavage” refers to the breakage of the covalent backbone of a DNAmolecule. Cleavage can be initiated by a variety of methods including,but not limited to, enzymatic or chemical hydrolysis of a phosphodiesterbond. Both single-stranded cleavage and double-stranded cleavage arepossible, and double-stranded cleavage can occur as a result of twodistinct single-stranded cleavage events. DNA cleavage can result in theproduction of either blunt ends or staggered ends. In certainembodiments, fusion polypeptides are used for targeted double-strandedDNA cleavage.

A “cleavage half-domain” is a polypeptide sequence which, in conjunctionwith a second polypeptide (either identical or different) forms acomplex having cleavage activity (preferably double-strand cleavageactivity). The terms “first and second cleavage half-domains;” “+ and −cleavage half-domains” and “right and left cleavage half-domains” areused interchangeably to refer to pairs of cleavage half-domains thatdimerize.

An “engineered cleavage half-domain” is a cleavage half-domain that hasbeen modified so as to form obligate heterodimers with another cleavagehalf-domain (e.g., another engineered cleavage half-domain). See, also,U.S. Patent Publication Nos. 20050064474, 20070218528, 20080131962, and20110201055 incorporated herein by reference in their entireties.

The term “sequence” refers to a nucleotide sequence of any length, whichcan be DNA or RNA; can be linear, circular or branched and can be eithersingle-stranded or double stranded. The terms “transgene” and “donorsequence” refers to a nucleotide sequence that is inserted into agenome. A donor sequence can be of any length, for example between 2 and10,000 nucleotides in length (or any integer value therebetween orthereabove), preferably between about 100 and 1,000 nucleotides inlength (or any integer therebetween), more preferably between about 200and 500 nucleotides in length.

“Chromatin” is the nucleoprotein structure comprising the cellulargenome. Cellular chromatin comprises nucleic acid, primarily DNA, andprotein, including histones and non-histone chromosomal proteins. Themajority of eukaryotic cellular chromatin exists in the form ofnucleosomes, wherein a nucleosome core comprises approximately 150 basepairs of DNA associated with an octamer comprising two each of histonesH2A, H2B, H3 and H4; and linker DNA (of variable length depending on theorganism) extends between nucleosome cores. A molecule of histone H1 isgenerally associated with the linker DNA. For the purposes of thepresent disclosure, the term “chromatin” is meant to encompass all typesof cellular nucleoprotein, both prokaryotic and eukaryotic. Cellularchromatin includes both chromosomal and episomal chromatin.

A “chromosome,” is a chromatin complex comprising all or a portion ofthe genome of a cell. The genome of a cell is often characterized by itskaryotype, which is the collection of all the chromosomes that comprisethe genome of the cell. The genome of a cell can comprise one or morechromosomes.

An “episome” is a replicating nucleic acid, nucleoprotein complex orother structure comprising a nucleic acid that is not part of thechromosomal karyotype of a cell. Examples of episomes include plasmidsand certain viral genomes.

A “target site” or “target sequence” is a nucleic acid sequence thatdefines a portion of a nucleic acid to which a binding molecule willbind, provided sufficient conditions for binding exist.

An “exogenous” molecule is a molecule that is not normally present in acell, but can be introduced into a cell by one or more genetic,biochemical or other methods. “Normal presence in the cell” isdetermined with respect to the particular developmental stage andenvironmental conditions of the cell. Thus, for example, a molecule thatis present only during embryonic development of muscle is an exogenousmolecule with respect to an adult muscle cell. Similarly, a moleculeinduced by heat shock is an exogenous molecule with respect to anon-heat-shocked cell. An exogenous molecule can comprise, for example,a functioning version of a malfunctioning endogenous molecule or amalfunctioning version of a normally-functioning endogenous molecule.

An exogenous molecule can be, among other things, a small molecule, suchas is generated by a combinatorial chemistry process, or a macromoleculesuch as a protein, nucleic acid, carbohydrate, lipid, glycoprotein,lipoprotein, polysaccharide, any modified derivative of the abovemolecules, or any complex comprising one or more of the above molecules.Nucleic acids include DNA and RNA, can be single- or double-stranded;can be linear, branched or circular; and can be of any length. Nucleicacids include those capable of forming duplexes, as well astriplex-forming nucleic acids. See, for example, U.S. Pat. Nos.5,176,996 and 5,422,251. Proteins include, but are not limited to,DNA-binding proteins, transcription factors, chromatin remodelingfactors, methylated DNA binding proteins, polymerases, methylases,demethylases, acetylases, deacetylases, kinases, phosphatases,integrases, recombinases, ligases, topoisomerases, gyrases andhelicases.

An exogenous molecule can be the same type of molecule as an endogenousmolecule, e.g., an exogenous protein or nucleic acid. For example, anexogenous nucleic acid can comprise an infecting viral genome, a plasmidor episome introduced into a cell, or a chromosome that is not normallypresent in the cell. Methods for the introduction of exogenous moleculesinto cells are known to those of skill in the art and include, but arenot limited to, lipid-mediated transfer (i.e., liposomes, includingneutral and cationic lipids), electroporation, direct injection, cellfusion, particle bombardment, calcium phosphate co-precipitation,DEAE-dextran-mediated transfer and viral vector-mediated transfer. Anexogenous molecule can also be the same type of molecule as anendogenous molecule but derived from a different species than the cellis derived from. For example, a human nucleic acid sequence may beintroduced into a cell line originally derived from a mouse or hamster.

By contrast, an “endogenous” molecule is one that is normally present ina particular cell at a particular developmental stage under particularenvironmental conditions. For example, an endogenous nucleic acid cancomprise a chromosome, the genome of a mitochondrion, chloroplast orother organelle, or a naturally-occurring episomal nucleic acid.Additional endogenous molecules can include proteins, for example,transcription factors and enzymes.

A “fusion” molecule is a molecule in which two or more subunit moleculesare linked, preferably covalently. The subunit molecules can be the samechemical type of molecule, or can be different chemical types ofmolecules. Examples of the first type of fusion molecule include, butare not limited to, fusion proteins (for example, a fusion between a ZFPor TALE DNA-binding domain and one or more cleavage domain or otherfunctional domain) and fusion nucleic acids (for example, a nucleic acidencoding the fusion protein described supra). Examples of the secondtype of fusion molecule include, but are not limited to, a fusionbetween a triplex-forming nucleic acid and a polypeptide, and a fusionbetween a minor groove binder and a nucleic acid.

Expression of a fusion protein in a cell can result from delivery of thefusion protein to the cell or by delivery of a polynucleotide encodingthe fusion protein to a cell, wherein the polynucleotide is transcribed,and the transcript is translated, to generate the fusion protein.Trans-splicing, polypeptide cleavage and polypeptide ligation can alsobe involved in expression of a protein in a cell. Methods forpolynucleotide and polypeptide delivery to cells are presented elsewherein this disclosure.

A “gene,” for the purposes of the present disclosure, includes a DNAregion encoding a gene product (see infra), as well as all DNA regionswhich regulate the production of the gene product, whether or not suchregulatory sequences are adjacent to coding and/or transcribedsequences. Accordingly, a gene includes, but is not necessarily limitedto, promoter sequences, terminators, translational regulatory sequencessuch as ribosome binding sites and internal ribosome entry sites,enhancers, silencers, insulators, boundary elements, replicationorigins, matrix attachment sites and locus control regions.

“Gene expression” refers to the conversion of the information, containedin a gene, into a gene product. A gene product can be the directtranscriptional product of a gene (e.g., mRNA, tRNA, rRNA, antisenseRNA, ribozyme, structural RNA or any other type of RNA) or a proteinproduced by translation of an mRNA. Gene products also include RNAswhich are modified, by processes such as capping, polyadenylation,methylation, and editing, and proteins modified by, for example,methylation, acetylation, phosphorylation, ubiquitination,ADP-ribosylation, myristilation, and glycosylation.

“Modulation” of gene expression refers to a change in the activity of agene. Modulation of expression can include, but is not limited to, geneactivation and gene repression. Genome editing (e.g., cleavage,alteration, inactivation, random mutation) can be used to modulateexpression. Gene inactivation refers to any reduction in gene expressionas compared to a cell that does not include a ZFP or TALEN as describedherein. Thus, gene inactivation may be partial or complete.

A “region of interest” is any region of cellular chromatin, such as, forexample, a gene or a non-coding sequence within or adjacent to a gene,in which it is desirable to bind an exogenous molecule. Binding can befor the purposes of targeted DNA cleavage and/or targeted recombination.A region of interest can be present in a chromosome, an episome, anorganellar genome (e.g., mitochondrial, chloroplast), or an infectingviral genome, for example. A region of interest can be within the codingregion of a gene, within transcribed non-coding regions such as, forexample, leader sequences, trailer sequences or introns, or withinnon-transcribed regions, either upstream or downstream of the codingregion. A region of interest can be as small as a single nucleotide pairor up to 2,000 nucleotide pairs in length, or any integral value ofnucleotide pairs.

“Eukaryotic” cells include, but are not limited to, fungal cells (suchas yeast), plant cells, animal cells, mammalian cells and human cells(e.g., T-cells).

“Secretory tissues” are those tissues in an animal that secrete productsout of the individual cell into a lumen of some type which are typicallyderived from epithelium. Examples of secretory tissues that arelocalized to the gastrointestinal tract include the cells that line thegut, the pancreas, and the gallbladder. Other secretory tissues includethe liver, tissues associated with the eye and mucous membranes such assalivary glands, mammary glands, the prostate gland, the pituitary glandand other members of the endocrine system. Additionally, secretorytissues may be thought of as individual cells of a tissue type which arecapable of secretion.

The terms “operative linkage” and “operatively linked” (or “operablylinked”) are used interchangeably with reference to a juxtaposition oftwo or more components (such as sequence elements), in which thecomponents are arranged such that both components function normally andallow the possibility that at least one of the components can mediate afunction that is exerted upon at least one of the other components. Byway of illustration, a transcriptional regulatory sequence, such as apromoter, is operatively linked to a coding sequence if thetranscriptional regulatory sequence controls the level of transcriptionof the coding sequence in response to the presence or absence of one ormore transcriptional regulatory factors. A transcriptional regulatorysequence is generally operatively linked in cis with a coding sequence,but need not be directly adjacent to it. For example, an enhancer is atranscriptional regulatory sequence that is operatively linked to acoding sequence, even though they are not contiguous.

With respect to fusion polypeptides, the term “operatively linked” canrefer to the fact that each of the components performs the same functionin linkage to the other component as it would if it were not so linked.For example, with respect to a fusion polypeptide in which a ZFP or TALEDNA-binding domain is fused to functional domain (e.g., cleavage domain,activation domain, repression domain, etc.), the ZFP or TALE DNA-bindingdomain and the activation domain are in operative linkage if, in thefusion polypeptide, the ZFP or TALE DNA-binding domain portion is ableto bind its target site and/or its binding site, while the activationdomain is able to up-regulate gene expression. When a fusion polypeptidein which a ZFP or TALE DNA-binding domain is fused to a cleavage domain,the ZFP or TALE DNA-binding domain and the cleavage domain are inoperative linkage if, in the fusion polypeptide, the ZFP or TALEDNA-binding domain portion is able to bind its target site and/or itsbinding site, while the cleavage domain is able to cleave DNA in thevicinity of the target site.

A “functional fragment” of a protein, polypeptide or nucleic acid is aprotein, polypeptide or nucleic acid whose sequence is not identical tothe full-length protein, polypeptide or nucleic acid, yet retains thesame function as the full-length protein, polypeptide or nucleic acid. Afunctional fragment can possess more, fewer, or the same number ofresidues as the corresponding native molecule, and/or can contain one ormore amino acid or nucleotide substitutions. Methods for determining thefunction of a nucleic acid (e.g., coding function, ability to hybridizeto another nucleic acid) are well-known in the art. Similarly, methodsfor determining protein function are well-known. For example, theDNA-binding function of a polypeptide can be determined, for example, byfilter-binding, electrophoretic mobility-shift, or immunoprecipitationassays. DNA cleavage can be assayed by gel electrophoresis. See Ausubelet al., supra. The ability of a protein to interact with another proteincan be determined, for example, by co-immunoprecipitation, two-hybridassays or complementation, both genetic and biochemical. See, forexample, Fields et al. (1989) Nature 340:245-246; U.S. Pat. No.5,585,245 and PCT WO 98/44350.

A “vector” is capable of transferring gene sequences to target cells.Typically, “vector construct,” “expression vector,” and “gene transfervector,” mean any nucleic acid construct capable of directing theexpression of a gene of interest and which can transfer gene sequencesto target cells. Thus, the term includes cloning, and expressionvehicles, as well as integrating vectors.

A “reporter gene” or “reporter sequence” refers to any sequence thatproduces a protein product that is easily measured, preferably althoughnot necessarily in a routine assay. Suitable reporter genes include, butare not limited to, sequences encoding proteins that mediate antibioticresistance (e.g., ampicillin resistance, neomycin resistance, G418resistance, puromycin resistance), sequences encoding colored orfluorescent or luminescent proteins (e.g., green fluorescent protein,enhanced green fluorescent protein, red fluorescent protein,luciferase), and proteins which mediate enhanced cell growth and/or geneamplification (e.g., dihydrofolate reductase). Epitope tags include, forexample, one or more copies of FLAG, His, myc, Tap, HA or any detectableamino acid sequence. “Expression tags” include sequences that encodereporters that may be operably linked to a desired gene sequence inorder to monitor expression of the gene of interest.

Nucleases

Described herein are compositions, particularly nucleases, which areuseful targeting a gene for the insertion of a transgene, for example,nucleases that are specific for HPRT. In certain embodiments, thenuclease is naturally occurring. In other embodiments, the nuclease isnon-naturally occurring, i.e., engineered in the DNA-binding domainand/or cleavage domain. For example, the DNA-binding domain of anaturally-occurring nuclease may be altered to bind to a selected targetsite (e.g., a meganuclease that has been engineered to bind to sitedifferent than the cognate binding site). In other embodiments, thenuclease comprises heterologous DNA-binding and cleavage domains (e.g.,zinc finger nucleases; TAL-effector nucleases; meganuclease DNA-bindingdomains with heterologous cleavage domains).

A. DNA-Binding Domains

In certain embodiments, the nuclease is a meganuclease (homingendonuclease). Naturally-occurring meganucleases recognize 15-40base-pair cleavage sites and are commonly grouped into four families:the LAGLIDADG family (“LAGLIDADG” disclosed as SEQ ID NO: 165), theGIY-YIG family, the His-Cyst box family and the HNH family. Exemplaryhoming endonucleases include I-SceI, I-CeuI, PI-PspI, PI-Sce, I-SceIV,I-CsmI, I-PanI, I-SceII, I-PpoI, I-SceIII, I-CreI, I-TevI, I-TevII andI-TevIII. Their recognition sequences are known. See also U.S. Pat. No.5,420,032; U.S. Pat. No. 6,833,252; Belfort et al. (1997) Nucleic AcidsRes. 25:3379-3388; Dujon et al. (1989) Gene 82:115-118; Perler et al.(1994) Nucleic Acids Res. 22, 1125-1127; Jasin (1996) Trends Genet.12:224-228; Gimble et al. (1996) J. Mol. Biol. 263:163-180; Argast etal. (1998) J. Mol. Biol. 280:345-353 and the New England Biolabscatalogue.

In certain embodiments, the nuclease comprises an engineered(non-naturally occurring) homing endonuclease (meganuclease). Therecognition sequences of homing endonucleases and meganucleases such asI-SceI, I-CeuI, PI-PspI, PI-Sce, I-SceIV, I-CsmI, I-PanI, I-PpoI,I-SceIII, I-CreI, I-TevI, I-TevII and I-TevIII are known. See also U.S.Pat. No. 5,420,032; U.S. Pat. No. 6,833,252; Belfort et al. (1997)Nucleic Acids Res. 25:3379-3388; Dujon et al. (1989) Gene 82:115-118;Perler et al. (1994) Nucleic Acids Res. 22, 1125-1127; Jasin (1996)Trends Genet. 12:224-228; Gimble et al. (1996) J. Mol. Biol.263:163-180; Argast et al. (1998) J. Mol. Biol. 280:345-353 and the NewEngland Biolabs catalogue. In addition, the DNA-binding specificity ofhoming endonucleases and meganucleases can be engineered to bindnon-natural target sites. See, for example, Chevalier et al. (2002)Molec. Cell 10:895-905; Epinat et al. (2003) Nucleic Acids Res.31:2952-2962; Ashworth et al. (2006) Nature 441:656-659; Paques et al.(2007) Current Gene Therapy 7:49-66; U.S. Patent Publication No.20070117128. The DNA-binding domains of the homing endonucleases andmeganucleases may be altered in the context of the nuclease as a whole(i.e., such that the nuclease includes the cognate cleavage domain) ormay be fused to a heterologous cleavage domain.

In other embodiments, the DNA-binding domain comprises a naturallyoccurring or engineered (non-naturally occurring) TAL effector DNAbinding domain. See, e.g., U.S. Patent Publication No. 201103073,incorporated by reference in its entirety herein. The plant pathogenicbacteria of the genus Xanthomonas are known to cause many diseases inimportant crop plants. Pathogenicity of Xanthomonas depends on aconserved type III secretion (T3S) system which injects more than 25different effector proteins into the plant cell. Among these injectedproteins are transcription activator-like effectors (TALE) which mimicplant transcriptional activators and manipulate the plant transcriptome(see Kay et al (2007) Science 318:648-651). These proteins contain a DNAbinding domain and a transcriptional activation domain. One of the mostwell characterized TALEs is AvrBs3 from Xanthomonas campestgris pv.Vesicatoria (see Bonas et al (1989) Mol Gen Genet 218: 127-136 andWO2010079430). TALEs contain a centralized domain of tandem repeats,each repeat containing approximately 34 amino acids, which are key tothe DNA binding specificity of these proteins. In addition, they containa nuclear localization sequence and an acidic transcriptional activationdomain (for a review see Schornack S, et al (2006) J Plant Physiol163(3): 256-272). In addition, in the phytopathogenic bacteria Ralstoniasolanacearum two genes, designated brg11 and hpx17 have been found thatare homologous to the AvrBs3 family of Xanthomonas in the R.solanacearum biovar 1 strain GMI1000 and in the biovar 4 strain RS1000(See Heuer et al (2007) Appl and Envir Micro 73(13): 4379-4384). Thesegenes are 98.9% identical in nucleotide sequence to each other butdiffer by a deletion of 1,575 bp in the repeat domain of hpx17. However,both gene products have less than 40% sequence identity with AvrBs3family proteins of Xanthomonas.

Thus, in some embodiments, the DNA binding domain that binds to a targetsite a HPRT gene is an engineered domain from a TAL effector similar tothose derived from the plant pathogens Xanthomonas (see Boch et al,(2009) Science 326: 1509-1512 and Moscou and Bogdanove, (2009) Science326: 1501) and Ralstonia (see Heuer et al (2007) Applied andEnvironmental Microbiology 73(13): 4379-4384); U.S. Patent PublicationNos. 20110301073 and 20110145940.

In certain embodiments, the DNA binding domain that binds to a targetsite a HPRT gene comprises a zinc finger protein. Preferably, the zincfinger protein is non-naturally occurring in that it is engineered tobind to a target site of choice. See, for example, See, for example,Beerli et al. (2002) Nature Biotechnol. 20:135-141; Pabo et al. (2001)Ann. Rev. Biochem. 70:313-340; Isalan et al. (2001) Nature Biotechnol.19:656-660; Segal et al. (2001) Curr. Opin. Biotechnol. 12:632-637; Chooet al. (2000) Curr. Opin. Struct. Biol. 10:411-416; U.S. Pat. Nos.6,453,242; 6,534,261; 6,599,692; 6,503,717; 6,689,558; 7,030,215;6,794,136; 7,067,317; 7,262,054; 7,070,934; 7,361,635; 7,253,273; andU.S. Patent Publication Nos. 2005/0064474; 2007/0218528; 2005/0267061,all incorporated herein by reference in their entireties.

An engineered zinc finger binding domain can have a novel bindingspecificity, compared to a naturally-occurring zinc finger protein.Engineering methods include, but are not limited to, rational design andvarious types of selection. Rational design includes, for example, usingdatabases comprising triplet (or quadruplet) nucleotide sequences andindividual zinc finger amino acid sequences, in which each triplet orquadruplet nucleotide sequence is associated with one or more amino acidsequences of zinc fingers which bind the particular triplet orquadruplet sequence. See, for example, co-owned U.S. Pat. Nos. 6,453,242and 6,534,261, incorporated by reference herein in their entireties.

Exemplary selection methods, including phage display and two-hybridsystems, are disclosed in U.S. Pat. Nos. 5,789,538; 5,925,523;6,007,988; 6,013,453; 6,410,248; 6,140,466; 6,200,759; and 6,242,568; aswell as WO 98/37186; WO 98/53057; WO 00/27878; WO 01/88197 and GB2,338,237. In addition, enhancement of binding specificity for zincfinger binding domains has been described, for example, in co-owned WO02/077227.

In addition, as disclosed in these and other references, DNA domains(e.g., multi-fingered zinc finger proteins) may be linked together usingany suitable linker sequences, including for example, linkers of 5 ormore amino acids in length. See, also, U.S. Pat. Nos. 6,479,626;6,903,185; and 7,153,949 for exemplary linker sequences 6 or more aminoacids in length. The zinc finger proteins described herein may includeany combination of suitable linkers between the individual zinc fingersof the protein. In addition, enhancement of binding specificity for zincfinger binding domains has been described, for example, in co-owned WO02/077227.

Selection of target sites; DNA-binding domains and methods for designand construction of fusion proteins (and polynucleotides encoding same)are known to those of skill in the art and described in detail in U.S.Pat. Nos. 6,140,081; 5,789,538; 6,453,242; 6,534,261; 5,925,523;6,007,988; 6,013,453; 6,200,759; WO 95/19431; WO 96/06166; WO 98/53057;WO 98/54311; WO 00/27878; WO 01/60970 WO 01/88197; WO 02/099084; WO98/53058; WO 98/53059; WO 98/53060; WO 02/016536 and WO 03/016496.

In addition, as disclosed in these and other references, zinc fingerdomains and/or multi-fingered zinc finger proteins may be linkedtogether using any suitable linker sequences, including for example,linkers of 5 or more amino acids in length. See, also, U.S. Pat. Nos.6,479,626; 6,903,185; and 7,153,949 for exemplary linker sequences 6 ormore amino acids in length. The proteins described herein may includeany combination of suitable linkers between the individual zinc fingersof the protein.

B. Cleavage Domains

Any suitable cleavage domain can be operatively linked to a DNA-bindingdomain to form a nuclease. For example, ZFP DNA-binding domains havebeen fused to nuclease domains to create ZFNs—a functional entity thatis able to recognize its intended nucleic acid target through itsengineered (ZFP) DNA binding domain and cause the DNA to be cut near theZFP binding site via the nuclease activity. See, e.g., Kim et al. (1996)Proc Nat'l Acad Sci USA 93(3):1156-1160. TALE proteins can also be fusedto nuclease domains to create site-specific TALE nucleases (TALENs).ZFNs and TALENs have been used for genome modification in a variety oforganisms. See, for example, United States Patent Publications20030232410; 20050208489; 20050026157; 20050064474; 20060188987;20060063231; 20110301073 and International Publication WO 07/014,275.

As noted above, the cleavage domain may be heterologous to theDNA-binding domain, for example a zinc finger DNA-binding domain and acleavage domain from a nuclease or a TALEN DNA-binding domain and acleavage domain, or meganuclease DNA-binding domain and cleavage domainfrom a different nuclease. Heterologous cleavage domains can be obtainedfrom any endonuclease or exonuclease. Exemplary endonucleases from whicha cleavage domain can be derived include, but are not limited to,restriction endonucleases and homing endonucleases. See, for example,2002-2003 Catalogue, New England Biolabs, Beverly, Mass.; and Belfort etal. (1997) Nucleic Acids Res. 25:3379-3388. Additional enzymes whichcleave DNA are known (e.g., S1 Nuclease; mung bean nuclease; pancreaticDNase I; micrococcal nuclease; yeast HO endonuclease; see also Linn etal. (eds.) Nucleases, Cold Spring Harbor Laboratory Press, 1993). One ormore of these enzymes (or functional fragments thereof) can be used as asource of cleavage domains and cleavage half-domains.

Similarly, a cleavage half-domain can be derived from any nuclease orportion thereof, as set forth above, that requires dimerization forcleavage activity. In general, two fusion proteins are required forcleavage if the fusion proteins comprise cleavage half-domains.Alternatively, a single protein comprising two cleavage half-domains canbe used. The two cleavage half-domains can be derived from the sameendonuclease (or functional fragments thereof), or each cleavagehalf-domain can be derived from a different endonuclease (or functionalfragments thereof). In addition, the target sites for the two fusionproteins are preferably disposed, with respect to each other, such thatbinding of the two fusion proteins to their respective target sitesplaces the cleavage half-domains in a spatial orientation to each otherthat allows the cleavage half-domains to form a functional cleavagedomain, e.g., by dimerizing. Thus, in certain embodiments, the nearedges of the target sites are separated by 5-8 nucleotides or by 15-18nucleotides. However any integral number of nucleotides or nucleotidepairs can intervene between two target sites (e.g., from 2 to 50nucleotide pairs or more). In general, the site of cleavage lies betweenthe target sites.

Restriction endonucleases (restriction enzymes) are present in manyspecies and are capable of sequence-specific binding to DNA (at arecognition site), and cleaving DNA at or near the site of binding.Certain restriction enzymes (e.g., Type IIS) cleave DNA at sites removedfrom the recognition site and have separable binding and cleavagedomains. For example, the Type IIS enzyme Fok I catalyzesdouble-stranded cleavage of DNA, at 9 nucleotides from its recognitionsite on one strand and 13 nucleotides from its recognition site on theother. See, for example, U.S. Pat. Nos. 5,356,802; 5,436,150 and5,487,994; as well as Li et al. (1992) Proc. Natl. Acad. Sci. USA89:4275-4279; Li et al. (1993) Proc. Natl. Acad. Sci. USA 90:2764-2768;Kim et al. (1994a) Proc. Natl. Acad. Sci. USA 91:883-887; Kim et al.(1994b) J. Biol. Chem. 269:31,978-31,982. Thus, in one embodiment,fusion proteins comprise the cleavage domain (or cleavage half-domain)from at least one Type IIS restriction enzyme and one or more zincfinger binding domains, which may or may not be engineered.

An exemplary Type IIS restriction enzyme, whose cleavage domain isseparable from the binding domain, is Fok I. This particular enzyme isactive as a dimer Bitinaite et al. (1998) Proc. Natl. Acad. Sci. USA 95:10,570-10,575. Accordingly, for the purposes of the present disclosure,the portion of the Fok I enzyme used in the disclosed fusion proteins isconsidered a cleavage half-domain. Thus, for targeted double-strandedcleavage and/or targeted replacement of cellular sequences using zincfinger-Fok I fusions, two fusion proteins, each comprising a FokIcleavage half-domain, can be used to reconstitute a catalytically activecleavage domain. Alternatively, a single polypeptide molecule containinga DNA binding domain and two Fok I cleavage half-domains can also beused.

A cleavage domain or cleavage half-domain can be any portion of aprotein that retains cleavage activity, or that retains the ability tomultimerize (e.g., dimerize) to form a functional cleavage domain.

Exemplary Type IIS restriction enzymes are described in InternationalPublication WO 07/014,275, incorporated herein in its entirety.Additional restriction enzymes also contain separable binding andcleavage domains, and these are contemplated by the present disclosure.See, for example, Roberts et al. (2003) Nucleic Acids Res. 31:418-420.

In certain embodiments, the cleavage domain comprises one or moreengineered cleavage half-domain (also referred to as dimerization domainmutants) that minimize or prevent homodimerization, as described, forexample, in U.S. Patent Publication Nos. 20050064474; 20060188987 and20080131962, the disclosures of all of which are incorporated byreference in their entireties herein. Amino acid residues at positions446, 447, 479, 483, 484, 486, 487, 490, 491, 496, 498, 499, 500, 531,534, 537, and 538 of Fok I are all targets for influencing dimerizationof the Fok I cleavage half-domains. See, also, U.S. Patent PublicationNos. 20050064474, 20070218528, 20080131962, and 20110201055

Exemplary engineered cleavage half-domains of Fok I that form obligateheterodimers include a pair in which a first cleavage half-domainincludes mutations at amino acid residues at positions 490 and 538 ofFok I and a second cleavage half-domain includes mutations at amino acidresidues 486 and 499.

Thus, in one embodiment, a mutation at 490 replaces Glu (E) with Lys(K); the mutation at 538 replaces Iso (I) with Lys (K); the mutation at486 replaced Gln (Q) with Glu (E); and the mutation at position 499replaces Iso (I) with Lys (K). Specifically, the engineered cleavagehalf-domains described herein were prepared by mutating positions 490(E→K) and 538 (I→K) in one cleavage half-domain to produce an engineeredcleavage half-domain designated “E490K:1538K” and by mutating positions486 (Q→E) and 499 (I→L) in another cleavage half-domain to produce anengineered cleavage half-domain designated “Q486E:I499L”. The engineeredcleavage half-domains described herein are obligate heterodimer mutantsin which aberrant cleavage is minimized or abolished. See, e.g., U.S.Patent Publication No. 2008/0131962, the disclosure of which isincorporated by reference in its entirety for all purposes.

In certain embodiments, the engineered cleavage half-domain comprisesmutations at positions 486, 499 and 496 (numbered relative to wild-typeFokI), for instance mutations that replace the wild type Gln (Q) residueat position 486 with a Glu (E) residue, the wild type Iso (I) residue atposition 499 with a Leu (L) residue and the wild-type Asn (N) residue atposition 496 with an Asp (D) or Glu (E) residue (also referred to as a“ELD” and “ELE” domains, respectively). In other embodiments, theengineered cleavage half-domain comprises mutations at positions 490,538 and 537 (numbered relative to wild-type FokI), for instancemutations that replace the wild type Glu (E) residue at position 490with a Lys (K) residue, the wild type Iso (I) residue at position 538with a Lys (K) residue, and the wild-type His (H) residue at position537 with a Lys (K) residue or a Arg (R) residue (also referred to as“KKK” and “KKR” domains, respectively). In other embodiments, theengineered cleavage half-domain comprises mutations at positions 490 and537 (numbered relative to wild-type FokI), for instance mutations thatreplace the wild type Glu (E) residue at position 490 with a Lys (K)residue and the wild-type His (H) residue at position 537 with a Lys (K)residue or a Arg (R) residue (also referred to as “KIK” and “KIR”domains, respectively). (See U.S. application Ser. No. 12/931,660). Instill further embodiments, the engineered cleavage half domains comprisemutations such that a nuclease pair is made with one H537R-R487D-N496D(“RDD”) FokI half domain and one N496D-D483R-H537R (“DRR”) FokI halfdomain. See, e.g., U.S. Patent Publication No. 20110201055.

Engineered cleavage half-domains described herein can be prepared usingany suitable method, for example, by site-directed mutagenesis ofwild-type cleavage half-domains (Fok I) as described in U.S. PatentPublication Nos. 20050064474 and 20080131962.

Alternatively, nucleases may be assembled in vivo at the nucleic acidtarget site using so-called “split-enzyme” technology (see e.g. U.S.Patent Publication No. 20090068164). Components of such split enzymesmay be expressed either on separate expression constructs, or can belinked in one open reading frame where the individual components areseparated, for example, by a self-cleaving 2A peptide or IRES sequence.Components may be individual zinc finger binding domains or domains of ameganuclease nucleic acid binding domain.

Nucleases can be screened for activity prior to use, for example in ayeast-based chromosomal system as described in WO 2009/042163 and20090068164. Nuclease expression constructs can be readily designedusing methods known in the art. See, e.g., United States PatentPublications 20030232410; 20050208489; 20050026157; 20050064474;20060188987; 20060063231; and International Publication WO 07/014,275.Expression of the nuclease may be under the control of a constitutivepromoter or an inducible promoter, for example the galactokinasepromoter which is activated (de-repressed) in the presence of raffinoseand/or galactose and repressed in presence of glucose.

Target Sites

As described in detail above, DNA domains can be engineered to bind toany sequence of choice in a locus, for example an HPRT gene. Anengineered DNA-binding domain can have a novel binding specificity,compared to a naturally-occurring DNA-binding domain Engineering methodsinclude, but are not limited to, rational design and various types ofselection. Rational design includes, for example, using databasescomprising triplet (or quadruplet) nucleotide sequences and individual(e.g., zinc finger) amino acid sequences, in which each triplet orquadruplet nucleotide sequence is associated with one or more amino acidsequences of DNA binding domain which bind the particular triplet orquadruplet sequence. See, for example, co-owned U.S. Pat. Nos. 6,453,242and 6,534,261, incorporated by reference herein in their entireties.Rational design of TAL-effector domains can also be performed. See,e.g., U.S. Patent Publication No. 20110301073.

Exemplary selection methods applicable to DNA-binding domains, includingphage display and two-hybrid systems, are disclosed in U.S. Pat. Nos.5,789,538; 5,925,523; 6,007,988; 6,013,453; 6,410,248; 6,140,466;6,200,759; and 6,242,568; as well as WO 98/37186; WO 98/53057; WO00/27878; WO 01/88197 and GB 2,338,237.

Selection of target sites; nucleases and methods for design andconstruction of fusion proteins (and polynucleotides encoding same) areknown to those of skill in the art and described in detail in U.S.Patent Application Publication Nos. 20050064474; 20060188987 and20110301073, incorporated by reference in their entireties herein.

In addition, as disclosed in these and other references, DNA-bindingdomains (e.g., multi-fingered zinc finger proteins) may be linkedtogether using any suitable linker sequences, including for example,linkers of 5 or more amino acids. See, e.g., U.S. Pat. Nos. 6,479,626;6,903,185; and 7,153,949 for exemplary linker sequences 6 or more aminoacids in length. The proteins described herein may include anycombination of suitable linkers between the individual DNA-bindingdomains of the protein. See, also, U.S. Provisional Patent PublicationNo. 20110287512.

Donors

As noted above, insertion of an exogenous sequence (also called a “donorsequence” or “donor” or “transgene”), for example for correction of amutant gene or for increased expression of a wild-type gene. It will bereadily apparent that the donor sequence is typically not identical tothe genomic sequence where it is placed. A donor sequence can contain anon-homologous sequence flanked by two regions of homology to allow forefficient HDR at the location of interest. Additionally, donor sequencescan comprise a vector molecule containing sequences that are nothomologous to the region of interest in cellular chromatin. A donormolecule can contain several, discontinuous regions of homology tocellular chromatin. For example, for targeted insertion of sequences notnormally present in a region of interest, said sequences can be presentin a donor nucleic acid molecule and flanked by regions of homology tosequence in the region of interest.

The donor polynucleotide can be DNA or RNA and can be single-stranded ordouble-stranded and can be introduced into a cell in linear or circularform. See, e.g., U.S. Patent Publication Nos. 20100047805 and20110207221. In addition, a donor polynucleotide may be a single ordouble stranded oligonucleotide. If introduced in linear form, the endsof the donor sequence can be protected (e.g., from exonucleolyticdegradation) by methods known to those of skill in the art. For example,one or more dideoxynucleotide residues are added to the 3′ terminus of alinear molecule and/or self-complementary oligonucleotides are ligatedto one or both ends. See, for example, Chang et al. (1987) Proc. Natl.Acad. Sci. USA 84:4959-4963; Nehls et al. (1996) Science 272:886-889.Additional methods for protecting exogenous polynucleotides fromdegradation include, but are not limited to, addition of terminal aminogroup(s) and the use of modified internucleotide linkages such as, forexample, phosphorothioates, phosphoramidates, and O-methyl ribose ordeoxyribose residues. See, also, U.S. Patent Publication No.20110207221.

A polynucleotide can be introduced into a cell as part of a vectormolecule having additional sequences such as, for example, replicationorigins, promoters and genes encoding antibiotic resistance. Moreover,donor polynucleotides can be introduced as naked nucleic acid, asnucleic acid complexed with an agent such as a liposome or poloxamer, ora macromolecule such as a dendrimir (See Wijagkanalen et al (2011) PharmRes 28(7) p. 1500-19), or can be delivered by viruses (e.g., adenovirus,helper-dependent adenovirus, AAV, herpesvirus, retrovirus, lentivirusand integrase defective lentivirus (IDLV)).

The donor may be inserted so that its expression is driven by theendogenous promoter at the integration site, for example the promoterthat drives expression of the HPRT gene. However, the donor may comprisea promoter and/or enhancer, for example a constitutive promoter or aninducible or tissue specific promoter.

Furthermore, although not required for expression, exogenous sequencesmay also be transcriptional or translational regulatory sequences, forexample, promoters, enhancers, insulators, internal ribosome entrysites, sequences encoding 2A peptides and/or polyadenylation signals.

Delivery

The nucleases, polynucleotides encoding these nucleases, donorpolynucleotides and compositions comprising the proteins and/orpolynucleotides described herein may be delivered in vivo or ex vivo byany suitable means.

Methods of delivering nucleases as described herein are described, forexample, in U.S. Pat. Nos. 6,453,242; 6,503,717; 6,534,261; 6,599,692;6,607,882; 6,689,558; 6,824,978; 6,933,113; 6,979,539; 7,013,219; and7,163,824, the disclosures of all of which are incorporated by referenceherein in their entireties.

Nucleases and/or donor constructs as described herein may also bedelivered using vectors containing sequences encoding one or more of thezinc finger or TALEN protein(s). Any vector systems may be usedincluding, but not limited to, plasmid vectors, retroviral vectors,lentiviral vectors, adenovirus vectors, helper-dependent adenovirus,poxvirus vectors; herpesvirus vectors and adeno-associated virusvectors, etc. See, also, U.S. Pat. Nos. 6,534,261; 6,607,882; 6,824,978;6,933,113; 6,979,539; 7,013,219; and 7,163,824, incorporated byreference herein in their entireties. Furthermore, it will be apparentthat any of these vectors may comprise one or more of the sequencesneeded for treatment. Thus, when one or more nucleases and a donorconstruct are introduced into the cell, the nucleases and/or donorpolynucleotide may be carried on the same vector or on differentvectors. When multiple vectors are used, each vector may comprise asequence encoding one or multiple nucleases and/or donor constructs.

Conventional viral and non-viral based gene transfer methods can be usedto introduce nucleic acids encoding nucleases and donor constructs incells (e.g., mammalian cells) and target tissues. Non-viral vectordelivery systems include DNA plasmids, naked nucleic acid, and nucleicacid complexed with a delivery vehicle such as a liposome or poloxamer.Viral vector delivery systems include DNA and RNA viruses, which haveeither episomal or integrated genomes after delivery to the cell. For areview of gene therapy procedures, see Anderson, Science 256:808-813(1992); Nabel & Felgner, TIBTECH 11:211-217 (1993); Mitani & Caskey,TIBTECH 11:162-166 (1993); Dillon, TIBTECH 11:167-175 (1993); Miller,Nature 357:455-460 (1992); Van Brunt, Biotechnology 6(10):1149-1154(1988); Vigne, Restorative Neurology and Neuroscience 8:35-36 (1995);Kremer & Perricaudet, British Medical Bulletin 51(1):31-44 (1995);Haddada et al., in Current Topics in Microbiology and ImmunologyDoerfler and Bohm (eds.) (1995); and Yu et al., Gene Therapy 1:13-26(1994).

Methods of non-viral delivery of nucleic acids include electroporation,lipofection, microinjection, biolistics, virosomes, liposomes,immunoliposomes, dendrimers, polycation or lipid:nucleic acidconjugates, naked DNA, artificial virions, agent-enhanced uptake of DNAor use of macromolecules such as dendrimers (see Wijagkanalen et al(2011) Pharm Res 28(7) p. 1500-19). Sonoporation using, e.g., theSonitron 2000 system (Rich-Mar) can also be used for delivery of nucleicacids.

Additional exemplary nucleic acid delivery systems include thoseprovided by Amaxa Biosystems (Cologne, Germany), Maxcyte, Inc.(Rockville, Md.), BTX Molecular Delivery Systems (Holliston, Mass.) andCopernicus Therapeutics Inc, (see for example U.S. Pat. No. 6,008,336).Lipofection is described in e.g., U.S. Pat. Nos. 5,049,386; 4,946,787;and 4,897,355) and lipofection reagents are sold commercially (e.g.,Transfectam™ and Lipofectin™). Cationic and neutral lipids that aresuitable for efficient receptor-recognition lipofection ofpolynucleotides include those of Feigner, WO 91/17424, WO 91/16024.

The preparation of lipid:nucleic acid complexes, including targetedliposomes such as immunolipid complexes, is well known to one of skillin the art (see, e.g., Crystal, Science 270:404-410 (1995); Blaese etal., Cancer Gene Ther. 2:291-297 (1995); Behr et al., Bioconjugate Chem.5:382-389 (1994); Remy et al., Bioconjugate Chem. 5:647-654 (1994); Gaoet al., Gene Therapy 2:710-722 (1995); Ahmad et al., Cancer Res.52:4817-4820 (1992); U.S. Pat. Nos. 4,186,183, 4,217,344, 4,235,871,4,261,975, 4,485,054, 4,501,728, 4,774,085, 4,837,028, and 4,946,787).

Additional methods of delivery include the use of packaging the nucleicacids to be delivered into EnGeneIC delivery vehicles (EDVs). These EDVsare specifically delivered to target tissues using bispecific antibodieswhere one arm of the antibody has specificity for the target tissue andthe other has specificity for the EDV. The antibody brings the EDVs tothe target cell surface and then the EDV is brought into the cell byendocytosis. Once in the cell, the contents are released (see MacDiarmidet al (2009) Nature Biotechnology 27(7):643).

The use of RNA or DNA viral based systems for the delivery of nucleicacids encoding engineered ZFPs take advantage of highly evolvedprocesses for targeting a virus to specific cells in the body andtrafficking the viral payload to the nucleus. Viral vectors can beadministered directly to patients (in vivo) or they can be used to treatcells in vitro and the modified cells are administered to patients (exvivo). Conventional viral based systems for the delivery of ZFPsinclude, but are not limited to, retroviral, lentivirus, adenoviral,adeno-associated, vaccinia and herpes simplex virus vectors for genetransfer. Integration in the host genome is possible with theretrovirus, lentivirus, and adeno-associated virus gene transfermethods, often resulting in long term expression of the insertedtransgene. Additionally, high transduction efficiencies have beenobserved in many different cell types and target tissues.

The tropism of a retrovirus can be altered by incorporating foreignenvelope proteins, expanding the potential target population of targetcells. Lentiviral vectors are retroviral vectors that are able totransduce or infect non-dividing cells and typically produce high viraltiters. Selection of a retroviral gene transfer system depends on thetarget tissue. Retroviral vectors are comprised of cis-acting longterminal repeats with packaging capacity for up to 6-10 kb of foreignsequence. The minimum cis-acting LTRs are sufficient for replication andpackaging of the vectors, which are then used to integrate thetherapeutic gene into the target cell to provide permanent transgeneexpression. Widely used retroviral vectors include those based uponmurine leukemia virus (MuLV), gibbon ape leukemia virus (GaLV), SimianImmunodeficiency virus (SIV), human immunodeficiency virus (HIV), andcombinations thereof (see, e.g., Buchscher et al., J. Virol.66:2731-2739 (1992); Johann et al., J. Virol. 66:1635-1640 (1992);Sommerfelt et al., Virol. 176:58-59 (1990); Wilson et al., J. Virol.63:2374-2378 (1989); Miller et al., J. Virol. 65:2220-2224 (1991);PCT/US94/05700).

In applications in which transient expression is preferred, adenoviralbased systems can be used. Adenoviral based vectors are capable of veryhigh transduction efficiency in many cell types and do not require celldivision. With such vectors, high titer and high levels of expressionhave been obtained. This vector can be produced in large quantities in arelatively simple system. Adeno-associated virus (“AAV”) vectors arealso used to transduce cells with target nucleic acids, e.g., in the invitro production of nucleic acids and peptides, and for in vivo and exvivo gene therapy procedures (see, e.g., West et al., Virology 160:38-47(1987); U.S. Pat. No. 4,797,368; WO 93/24641; Kotin, Human Gene Therapy5:793-801 (1994); Muzyczka, J. Clin. Invest. 94:1351 (1994).Construction of recombinant AAV vectors are described in a number ofpublications, including U.S. Pat. No. 5,173,414; Tratschin et al., Mol.Cell. Biol. 5:3251-3260 (1985); Tratschin, et al., Mol. Cell. Biol.4:2072-2081 (1984); Hermonat & Muzyczka, PNAS 81:6466-6470 (1984); andSamulski et al., J. Virol. 63:03822-3828 (1989).

At least six viral vector approaches are currently available for genetransfer in clinical trials, which utilize approaches that involvecomplementation of defective vectors by genes inserted into helper celllines to generate the transducing agent.

pLASN and MFG-S are examples of retroviral vectors that have been usedin clinical trials (Dunbar et al., Blood 85:3048-305 (1995); Kohn etal., Nat. Med. 1:1017-102 (1995); Malech et al., PNAS 94:22 12133-12138(1997)). PA317/pLASN was the first therapeutic vector used in a genetherapy trial. (Blaese et al., Science 270:475-480 (1995)). Transductionefficiencies of 50% or greater have been observed for MFG-S packagedvectors. (Ellem et al., Immunol Immunother. 44(1):10-20 (1997); Dranoffet al., Hum. Gene Ther. 1:111-2 (1997).

Recombinant adeno-associated virus vectors (rAAV) are a promisingalternative gene delivery systems based on the defective andnonpathogenic parvovirus adeno-associated type 2 virus. All vectors arederived from a plasmid that retains only the AAV 145 bp invertedterminal repeats flanking the transgene expression cassette. Efficientgene transfer and stable transgene delivery due to integration into thegenomes of the transduced cell are key features for this vector system.(Wagner et al., Lancet 351:9117 1702-3 (1998), Kearns et al., Gene Ther.9:748-55 (1996)). Any other AAV serotypes, including AAV1, AAV3, AAV4,AAV5, AAV6, AAV8, AAV9 and AAVrh10 can also be used in accordance withthe present invention.

Replication-deficient recombinant adenoviral vectors (Ad) can beproduced at high titer and readily infect a number of different celltypes. Most adenovirus vectors are engineered such that a transgenereplaces the Ad E1a, E1b, and/or E3 genes; subsequently the replicationdefective vector is propagated in human 293 cells that supply deletedgene function in trans. Ad vectors can transduce multiple types oftissues in vivo, including non-dividing, differentiated cells such asthose found in liver, kidney and muscle. Conventional Ad vectors have alarge carrying capacity. An example of the use of an Ad vector in aclinical trial involved polynucleotide therapy for anti-tumorimmunization with intramuscular injection (Sterman et al., Hum. GeneTher. 7:1083-9 (1998)). Additional examples of the use of adenovirusvectors for gene transfer in clinical trials include Rosenecker et al.,Infection 24:1 5-10 (1996); Sterman et al., Hum. Gene Ther. 9:71083-1089 (1998); Welsh et al., Hum. Gene Ther. 2:205-18 (1995); Alvarezet al., Hum. Gene Ther. 5:597-613 (1997); Topf et al., Gene Ther.5:507-513 (1998); Sterman et al., Hum. Gene Ther. 7:1083-1089 (1998).

Packaging cells are used to form virus particles that are capable ofinfecting a host cell. Such cells include 293 cells, which packageadenovirus, and ψ2 cells or PA317 cells, which package retrovirus. Viralvectors used in gene therapy are usually generated by a producer cellline that packages a nucleic acid vector into a viral particle. Thevectors typically contain the minimal viral sequences required forpackaging and subsequent integration into a host (if applicable), otherviral sequences being replaced by an expression cassette encoding theprotein to be expressed. The missing viral functions are supplied intrans by the packaging cell line. For example, AAV vectors used in genetherapy typically only possess inverted terminal repeat (ITR) sequencesfrom the AAV genome which are required for packaging and integrationinto the host genome. Viral DNA is packaged in a cell line, whichcontains a helper plasmid encoding the other AAV genes, namely rep andcap, but lacking ITR sequences. The cell line is also infected withadenovirus as a helper. The helper virus promotes replication of the AAVvector and expression of AAV genes from the helper plasmid. The helperplasmid is not packaged in significant amounts due to a lack of ITRsequences. Contamination with adenovirus can be reduced by, e.g., heattreatment to which adenovirus is more sensitive than AAV.

In many gene therapy applications, it is desirable that the gene therapyvector be delivered with a high degree of specificity to a particulartissue type. Accordingly, a viral vector can be modified to havespecificity for a given cell type by expressing a ligand as a fusionprotein with a viral coat protein on the outer surface of the virus. Theligand is chosen to have affinity for a receptor known to be present onthe cell type of interest. For example, Han et al., Proc. Natl. Acad.Sci. USA 92:9747-9751 (1995), reported that Moloney murine leukemiavirus can be modified to express human heregulin fused to gp70, and therecombinant virus infects certain human breast cancer cells expressinghuman epidermal growth factor receptor. This principle can be extendedto other virus-target cell pairs, in which the target cell expresses areceptor and the virus expresses a fusion protein comprising a ligandfor the cell-surface receptor. For example, filamentous phage can beengineered to display antibody fragments (e.g., FAB or Fv) havingspecific binding affinity for virtually any chosen cellular receptor.Although the above description applies primarily to viral vectors, thesame principles can be applied to nonviral vectors. Such vectors can beengineered to contain specific uptake sequences which favor uptake byspecific target cells.

Gene therapy vectors can be delivered in vivo by administration to anindividual patient, typically by systemic administration (e.g.,intravenous, intraperitoneal, intramuscular, subdermal, or intracranialinfusion) or topical application, as described below. Alternatively,vectors can be delivered to cells ex vivo, such as cells explanted froman individual patient (e.g., lymphocytes, bone marrow aspirates, tissuebiopsy) or universal donor hematopoietic stem/progenitor cells, followedby reimplantation of the cells into a patient, usually after selectionfor cells which have incorporated the vector.

Vectors (e.g., retroviruses, adenoviruses, liposomes, etc.) containingnucleases and/or donor constructs can also be administered directly toan organism for transduction of cells in vivo. Alternatively, naked DNAcomplexed/formulated with a delivery vehicle (e.g. liposome orpoloxamer) can be administered. Administration is by any of the routesnormally used for introducing a molecule into ultimate contact withblood or tissue cells including, but not limited to, injection,infusion, topical application and electroporation. Suitable methods ofadministering such nucleic acids are available and well known to thoseof skill in the art, and, although more than one route can be used toadminister a particular composition, a particular route can oftenprovide a more immediate and more effective reaction than another route.

Vectors suitable for introduction of polynucleotides described hereininclude non-integrating lentivirus vectors or integrase defectivelentivirus (IDLV). See, for example, Ory et al. (1996) Proc. Natl. Acad.Sci. USA 93:11382-11388; Dull et al. (1998) J. Virol. 72:8463-8471;Zuffery et al. (1998) J. Virol. 72:9873-9880; Follenzi et al. (2000)Nature Genetics 25:217-222; U.S. Patent Publication No 2009/054985.

Pharmaceutically acceptable carriers are determined in part by theparticular composition being administered, as well as by the particularmethod used to administer the composition. Accordingly, there is a widevariety of suitable formulations of pharmaceutical compositionsavailable, as described below (see, e.g., Remington's PharmaceuticalSciences, 17th ed., 1989).

It will be apparent that the nuclease-encoding sequences and donorconstructs can be delivered using the same or different systems. Forexample, a donor polynucleotide can be carried by a plasmid, while theone or more nucleases can be carried by a AAV vector. Furthermore, thedifferent vectors can be administered by the same or different routes(intramuscular injection, tail vein injection, other intravenousinjection, intraperitoneal administration and/or intramuscularinjection. The vectors can be delivered simultaneously or in anysequential order.

Formulations for both ex vivo and in vivo administrations includesuspensions in liquid or emulsified liquids. The active ingredientsoften are mixed with excipients which are pharmaceutically acceptableand compatible with the active ingredient. Suitable excipients include,for example, water, saline, dextrose, glycerol, ethanol or the like, andcombinations thereof. In addition, the composition may contain minoramounts of auxiliary substances, such as, wetting or emulsifying agents,pH buffering agents, stabilizing agents or other reagents that enhancethe effectiveness of the pharmaceutical composition.

Applications

The methods and compositions of the invention can be used in anycircumstance wherein it is desired to perform genome editing in a cell.Editing can be in the form of knocking out a desired gene or locus, orcan encompass the targeted integration of a nucleic acid encoding atherapeutic transgene or structural nucleic acid such as an shRNA. Themethods and compositions of the invention can be used to select for atargeted integration into the HPRT locus and/or to select fornuclease-mediated modification (e.g., insertion, deletion, inactivation)at another locus, such as a specific gene or safe harbor, for example,or the knockout of HPRT can be used as a marker for introduction ofexpression vector(s) encoding engineered nucleases (transduction) and amarker for successful nuclease activity. A desired transgene can beintroduced directly into the HPRT locus, and the practitioner may selectfor integration by exposing the recipient cells to 6-TG. Alternatively,nucleases targeting HPRT may be introduced into a cell with another setof one or more engineered nucleases such that successful cleavage andknockout of HPRT may be used as a screen for cells with successfulcleavage at the one or more additional targeted (non-HPRT) loci.Similarly, donors for targeted integration may be also introduced viaone or more nucleases, and knockout of HPRT may be used as a screen forcells with successful nuclease activity, such that a pool of cellsenriched for cleavage is identified, increasing the likelihood ofcleavage at the alternative (non-HPRT) location(s). Knockout of aspecific gene or locus is advantageous for many different technologies.One or more genes of interest may be knocked out in cell or animalmodels to study the phenotypic or other effects. Other genome editingapproaches such as introduction of specific donor DNAs at specificlocations can also be used in cell and animal models.

Modified cells may be used therapeutically, containing knock outs ofspecific genes such as virus receptors and co-receptors (e.g. CCR5), orregulatory genes and their products (Bcl11A, EKLF), aberrant genes(globin, blood factors, genes involved in lysosomal storage diseases),specific nucleic acid targets (EKLF binding site), self markers (HLAgenes and their regulators), receptors such as endogenous T-cellreceptors, to name a few. Knockout can be done with cells removed from apatient in need where the cells are treated ex vivo (e.g. T or B cells),and then reintroduced back via infusion, or they may be kept andexpanded into a universal donor line. Stem or progenitor cells may beremoved and treated ex vivo and also given to a patient in need thereof,for example modified hematopoietic (CD34+) stem cells. Patient specificand modified iPSC can also be made and used for patient treatment.Additionally, knockout may be done in vivo using introduction of theengineered nucleases via any suitable delivery method, for example AAVSor adenoviral vectors.

Donor integration also has a great many applications. Similar to theuses mentioned above for knockouts, targeted integration can be used toadd gene(s) of interest at a desired location(s) including genecorrection at an endogenous gene and addition of a DNA cassette to asafe harbor. Donor molecules may encode gene products such astherapeutic proteins or structural nucleic acids (e.g. shRNA). Uses fordonors can include the addition of therapeutic products such as naturalproteins, engineered antibodies, chimeric antibody receptors (CARs) orengineered T cell receptors. These methods and compositions can be usedfor the treatment of cancers and the like. Corrected globin genes may beused for patients afflicted with diseases such as sickle cell anemia andcorrected common gamma chain genes can be introduced to treat patientswith X-linked severe combined immunodeficiency. Wild type genes encodingclotting factors may be used therapeutically for hemophilia patients.For example, wild type or an enhanced Factor VIII gene may be introducedin patients with Hemophilia A, or wild type or enhanced Factor IX genesmay be introduced in patients with Hemophilia B.

Additionally, genes involved in lysosomal storage diseases may be used.The most common examples of these diseases and the genes involved areGaucher's (glucocerebrosidase deficiency-gene name: GBA), Fabry's (agalactosidase deficiency-GLA), Hunter's (iduronate-2-sulfatasedeficiency—IDS), Hurler's (alpha-L iduronidase deficiency—IDUA), andNiemann-Pick's (sphingomyelin phosphodiesterase 1 deficiency-SMPD1)diseases. Alternatively, a wild type FoxB3 gene may be introduced inpatient stem cells isolated from patients afflicted with IPEX (immunedysregulation polyendocrinopathy enteropathy, X-linked, see van derVliet and Nieuwenhuis (2007) Clin Dev Immunol 2007:89017). In all thesenon-limiting examples, the donor DNAs can be introduced into the cellgenomes through HDR or NHEJ end-capture, depending on donor design.These treatments may be made ex vivo or in vivo, as described above.

The following Examples relate to exemplary embodiments of the presentdisclosure in which the nuclease comprises a zinc finger nuclease (ZFN)or a TALEN. It will be appreciated that this is for purposes ofexemplification only and that other nucleases can be used (e.g. homingendonucleases or meganucleases) with engineered DNA-binding domains andheterologous cleavage domains.

EXAMPLES Example 1 Design, Construction and General Characterization ofZinc Finger Protein Nucleases (ZFN)

Zinc finger proteins targeted to HPRT were designed and incorporatedinto plasmids, AAV or adenoviral vectors essentially as described inUrnov et al. (2005) Nature 435(7042):646-651, Perez et al (2008) NatureBiotechnology 26(7):808-816, and as described in U.S. Pat. No.6,534,261. Table 1 shows the recognition helices within the DNA bindingdomain of exemplary HPRT ZFPs while Table 2 shows the target sites forthese ZFPs (DNA target sites indicated in uppercase letters;non-contacted nucleotides indicated in lowercase). Nucleotides in thetarget site that are contacted by the ZFP recognition helices areindicated in uppercase letters; non-contacted nucleotides indicated inlowercase.

TABLE 1 Mouse and Human HPRT-specific zinc finger nucleases-helix designTarget species/ Design SBS # F1 F2 F3 F4 F5 F6 Mouse RSDALSR DRSALARRSDNLSQ ASNDRKK RSDNLSA RNNDRKT 29264 (SEQ ID (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID NO: 1) NO: 2) NO: 3) NO: 4) NO: 5) NO: 6) Mouse DRSHLSRDRSALAR RSDTLSE QSSHLAR RSDTLSQ TRQARIQ 29262 (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID (SEQ ID NO: 7) NO: 2) NO: 8) NO: 9) NO: 10) NO: 11)Human DRSHLTR QSGHLSR RSDSLSV RSANLTR RSDNLSE VRRALSS 29251 (SEQ ID(SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID NO: 12) NO: 13) NO: 14) NO: 15)NO: 16) NO: 17) Human RSDNLSE TSGSLTR DRSNLSR QRSNLDS RSDNLAR DQSYRRT29250 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID NO: 16) NO: 18)NO: 19) NO: 20) NO: 21) NO: 22) Human DRSHLTR QSGHLSR RSDSLSV RSAALARRSDNLSE VRRALSS 30179 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ IDNO: 12) NO: 13) NO: 14) NO: 23) NO: 16) NO: 17) Mouse/ RSDSLLR QSCARNVQSGNLAR QSTPRNK RSDALSE QNATRTK human (SEQ ID (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID 29223 NO: 24) NO: 25) NO: 26) NO: 27) NO: 28) NO: 29)Mouse/ DRSALTK RSDNLSE KRCNLRC DRSALSR QSGSLTR NA Human (SEQ ID (SEQ ID(SEQ ID (SEQ ID (SEQ ID 29216 NO: 30) NO: 16) NO: 31) NO: 32) NO: 33)Human DRSHLSR RSDDLTR RSDDLTR RSDDRKT NA NA 11447 (SEQ ID (SEQ ID(SEQ ID (SEQ ID NO: 7) NO: 34) NO: 34) NO: 35) Human RSDDLTR RSDALTQTSGSLSR DSSDRKK NA NA 11443 (SEQ ID (SEQ ID (SEQ ID (SEQ ID NO: 34)NO: 36) NO: 37) NO: 38) Human QSGHLAR QRVALQA QSSHLTR QSGSLTR RDSNLSVQKINLQV 34270 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID NO: 79)NO: 80) NO: 81) NO: 33) NO: 82) NO: 83) Human RSDVLSA QNATRIN QNATRINTSGNLTR QSNDLNS NA 34269 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID NO: 84)NO: 85) NO: 85) NO: 86) NO: 87) Human QSGNLAR QSGDLTR RSDTLSE ARSTRTNRSDSLSV RSAHLSR 34278 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ IDNO: 26) NO: 49) NO: 8) NO: 88) NO: 14) NO: 89) Human DRSNLSR QKVTLAAQSGNLAR QGANLIK DRSALSR QSGDLTR 34277 (SEQ ID (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID NO: 19) NO: 90) NO: 26) NO: 91) NO: 32) NO: 49) HumanTSGSLSR QSGNLAR QSSDLSR RSDHLSQ DNSNRIN NA 34306 (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID NO: 37) NO: 26) NO: 92) NO: 93) NO: 94) Human QSGDLTRTSGSLTR RSDVLSE RNQHRKT RSAHLSR DRSDLSR 34303 (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID (SEQ ID NO: 49) NO: 18) NO: 95) NO: 96) NO: 89) NO: 97)Human RSDNLSN TSSNRKN TSGNLTR WRSCLRA QSGNLAR NA 34321 (SEQ ID (SEQ ID(SEQ ID (SEQ ID (SEQ ID NO: 98) NO: 99) NO: 86) NO: 100) NO: 26) HumanQSSDLSR QSGNRTT TSSNLSR TSGNLTR LSQDLNR NA 35944 (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID NO: 92) NO: 101) NO: 102) NO: 86) NO: 103) Human NNRDLINTSSNLST HSNARKT QSGALAR RSDHLSR NA 35974 (SEQ ID (SEQ ID (SEQ ID (SEQ ID(SEQ ID NO: 104) NO: 105) NO: 106) NO: 107) NO: 108) Human ARSTRTNQSGHLAR QRVALQA ERGTLAR RSDALAR NA 35963 (SEQ ID (SEQ ID (SEQ ID (SEQ ID(SEQ ID NO: 88) NO: 79) NO: 80) NO: 109) NO: 110) Human DRSNLSR ARWYLDKRSANLTR RSDVLSE QRSNLKV NA 34359 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ IDNO: 19) NO: 111) NO: 15) NO: 95) NO: 112) Human RSDNLAR QKVNLRE QRTHLTQRSDNLSE TRSPLRN NA 35981 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID NO: 21)NO: 113) NO: 114) NO: 16) NO: 115) Human QSGHLAR QSSNRQK QSGHLAR QSGSLTRRSDNLSV QNANRIT 37714 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ IDNO: 79) NO: 116) NO: 79) NO: 33) NO: 117) NO: 118) Human RSDVLSA QNATRINQSGDLTR TSGNLTR QSNDLNS NA 37706 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ IDNO: 84) NO: 85) NO: 49) NO: 86) NO: 87) Human LKQHLNE QNAHRKT DSSHRTRRSDHLSQ CTRNRWR NA 37741 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ IDNO: 119) NO: 120) NO: 121) NO: 93) NO: 122) Human QSGDLTR TSGSLTRRSDVLSE RNQHRKT RSDHLSE HSRTRTK 37734 (SEQ ID (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID NO: 49) NO: 18) NO: 95) NO: 96) NO: 123) NO: 124) HumanTSGSLSR QAGQRRV DRSHLAR RSDHLSQ CTRNRWR NA 37746 (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID NO: 37) NO: 125) NO: 126) NO: 93) NO: 122) Human QSGDLTRTSGSLTR RSDVLSE RNQHRKT RSDHLSE HSRTRTK 37735 (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID (SEQ ID NO: 49) NO: 18) NO: 95) NO: 96) NO: 123)NO: 124)

TABLE 2 Target Sites of Mouse and Human HPRT-specificzinc finger nucleases SBS # Target site 29264 acCCGCAGTCCCAGcGTCGTGgtgag(SEQ ID NO: 39) cc_ 29262 gcATGACGGGACCGGTCGGCtcgcgg (SEQ ID NO: 40) ca_29251 tgATGAAGGAGATGGGAGGCcatcac (SEQ ID NO: 41) at 29250atCTCGAGCAAGACGTTCAGtoctac (SEQ ID NO: 42) ag_ 30179tgATGAAGGAGATGGGAGGCcatcac (SEQ ID NO: 41) at_ 29223aaGCACTGaATAGAAATAGTGataga (SEQ ID NO: 43) tc_ 29216atGTAATCCAGCAGGTCagcaaagaa (SEQ ID NO: 44) tt_ 11447ggCCGGCGcGCGGGCtgactgctcag (SEQ ID NO: 45) ga_ 11443gcTCCGTTATGGCGacccgcagccct (SEQ ID NO: 46) gg_ 34270tgCAAAAGGTAGGAAAAGGAccaaccag (SEQ ID NO: 166) 34269acCCAGATACAaACAATGgatagaaaac (SEQ ID NO: 167) 34278ctGGGATGaACTCTGgGCAGAAttcaca (SEQ ID NO: 127) 34277atGCAGTCTAAGAAtACAGACagatcag (SEQ ID NO: 128) 34306tgCACAGGgGCTGAAGTTgtcccacagg (SEQ ID NO: 129) 34303tgGCCAGGAGGCTGGTTGCAaacatttt (SEQ ID NO: 130) 34321ttGAATGTGATtTGAAAGgtaatttagt (SEQ ID NO: 131) 35944aaGCTGATGATtTAAGCTttggcggttt (SEQ ID NO: 132) 35974gtGGGGTAATTGATCCAtgtatgccatt (SEQ ID NO: 133) 35963ggGTGGCCAAAGGAACTgcgcgaacctc (SEQ ID NO: 134) 34359atCAACTGGAGTTGGACtgtaataccag (SEQ ID NO: 135) 35981ctTTACAGAGACAAGAGgaataaaggaa (SEQ ID NO: 136) 37714tgCAAAAGGTAGGAAAAGGAccaaccag (SEQ ID NO: 166) 37706acCCAGATACAaACAATGgatagaaaac (SEQ ID NO: 167) 37741tgCACAGGGGCTGAAGTtgtcccacagg (SEQ ID NO: 129) 37734tgGCCAGGAGGCTGGTTGCAaacatttt (SEQ ID NO: 130) 37746tgCACAGGGGCtGAAGTTgtcccacagg (SEQ ID NO: 129) 37735tgGCCAGGAGGCTGGTTGCAaacatttt (SEQ ID NO: 130)

Example 2 Activity of Murine and Human-Specific HPRT ZFNs

ZFN pairs targeting the murine or the human HPRT gene, as well as a ZFNpair designed to recognize conserved sequences in both the human andmurine HPRT gene were used to test the ability of these ZFNs to induceDSBs at a specific target site. In particular, the Cel-I mismatch assay(Surveyor™, Transgenomics; Perez et al, (2008) Nat. Biotechnol. 26:808-816 and Guschin et al, (2010) Methods Mol Biol. 649:247-56) was usedwhere PCR-amplification of the target site was followed byquantification of insertions and deletions (indels) using the mismatchdetecting enzyme Cel-I (Yang et al, (2000) Biochemistry 39, 3533-3541)which provides a lower-limit estimate of DSB frequency. Afterintroduction of the ZFN expression vector at standard conditions (37°C.) into human K562 cells or murine Neuro2A cells as described in Perez,ibid, genomic DNA was isolated from the cells using the DNeasy™ kit(Qiagen). The percent indels indicates the percentage of alleles thatwere altered by NHEJ following cleavage.

Results from the Cel-I mismatch assay on DNA isolated from K562 cellsamples (FIG. 1A) or Neuro 2A cell samples (FIG. 1B) demonstrate thatthe ZFNs cleave at their respective target sites. Lane identities are asshown, and the percent of PCR products wherein the nucleotides have beeninserted or deleted (“indels”) are indicated at the bottom of each lane(“% NHEJ”).

Example 3 Percent of Modified Cells Following ZFN Treatment andSelection on 6-TG

To test the frequency of targeted modification following selection ofthe transfected cells on 6-TG, cells were transfected with a combinationof HPRT-specific ZFNs (SBS #29251 and SBS #29250, see Table 1 above) andCCR5-specific ZFNs (SBS #8196z and SBS #8266, see co-owned patent U.S.Pat. No. 7,951,925).

Expression plasmids encoding the ZFNs were introduced into K562 cellsand three days after transfection, the cells were split into two pools.One pool was selected on a concentration of 6 μM 6-TG and then followingselection for 8-11 days, was analyzed by the Cel-I mismatch assay forthe presence of indels. The results are shown in FIG. 2. A comparison ofthe results from cells prior to 6-TG selection, with those selected on6-TG demonstrated a dramatic enrichment for modified cells. For example,cell pools that initially showed a detectable modification rate of 0-4.6percent prior to 6-TG selection were measured at 71-100% modificationafter selection. The PCR products from the 6-TG selected cells werecloned and sequenced, where the sequence analysis demonstrated amodification of all clones sequenced (88 of 88 clones modified).

Example 4 Use of 6-TG Selection for Enrichment of Cleavage at a SecondTarget Site

The concept that 6-TG selection can also be used to enrich formodification at a second locus by another ZFN pair that was introducedwith the HPRT-specific nucleases was then tested. We assumed that such a‘co-selection’ would be most efficient if the second ZFN pair wasprovided in excess of the HPRT ZFN pair and if the activity of the HPRTZFN pair was weaker than that of the second ZFN pair, which wasaccomplished by coupling the HPRT ZFN DNA binding domain in the pair tothe less active obligate heterodimeric Fok I nuclease domain mutants DDand RR while the DNA binding domains in the second (non-HPRT-targeted)ZFN pair was coupled to the ELD KKR mutant pair. (see co-owned US PatentPublication No. 2011/0201055 and 20110158957). This arrangement has theadditional advantage that the DD/RR mutants are orthologous to the moreactive heterodimeric ELD/KKR FokI mutants, which means that even thoughfour ZFNs are introduced into the cell concurrently, active dimeric ZFNpairs can only be formed from the two desired combinations.

FIG. 3 shows that upon introduction of the 29251/29250 HPRT ZFN pair anda ZFN pair targeting CCR5 into K562 cells, 6-TG selection results in adramatic enrichment of CCR5 modified cells, demonstrating the utility ofthe ‘co-selection approach’ for the enrichment of modification at asecond target locus. In this experiment, the CCR5-specific ZFNs usedwere 8196z and 8266, described above in Example 4, and modification atthe CCR5 locus was assayed by the Cel-I mismatch assay. In FIG. 3, abovethe boxed gel, the ngs of DNA used in the transfections are indicated.The double (“**”) or single (“*”) asterisks indicate that the FokIobligate heterodimeric pairs ELD/KKR or DD/RR are being used,respectively (see co-owned U.S. Patent Publication Nos. 20080131962 and20110201055 as well as U.S. Pat. No. 7,914,796). The lane with theexperiment number indicates the Cel-I mismatch assay results observedfrom DNA isolated from cells following recover from transfection, andthe (−) indicates the Cel-I mismatch assay results in DNA isolated fromcells grown in the absence of 6-TG, while the (+) indicates Cel-Imismatch assay results from DNA isolated from cells grown under the 6-TGselection. The numbers at the bottom of the lanes indicate the percentof NHEJ as measured by the Cel-I mismatch assay.

Example 5 Use of 6-TG Selection for Enrichment of Targeted DonorInsertion

Use of 6-TG selection in K562 cells transfected with the 29251/29250HPRT ZFN pair and a donor molecule carrying homology to the HPRT locusto enrich of cells that have undergone homologous recombination withintroduced the donor at the HPRT locus was also tested. In particular, adonor containing a BamHI restriction site targeted into the HPRT locuswas introduced using HPRT ZFNs as described above. In this experiment,three different types of plasmids carrying donor molecules with therestriction site were co-introduced with the nucleases: 8 μg of a donorDNA fragment with short regions (arms) of homology to the targeted HPRTinsertion site (359 nucleotides), 8 μg of the same donor but where thedonor plasmid contained an enhancer element, and 8 μg of a donor DNAfragment with a long arm of homology (725 nucleotides) to the insertionsite. The transfectants were allowed to recover following transfectionin the absence of any selection, and then split and grown either in thepresence (+) or absence (−) of 6-TG. DNA was isolated at day uponcompletion of selection (8-11 days) and the region surrounding theinsertion site was amplified by PCR. The PCR products were thensubjected to restriction digestion with the BamHI enzyme.

As shown in FIG. 4, donor integration was enriched up to 3-fold and upto levels exceeding 40% of the alleles when 6-TG selection was used.Numbers at the bottom of the lanes indicate the percent of the PCRproduct that was cut by the enzyme (“% cutting”). Up to 43% of the DNAcontained the donor DNA at the HPRT locus as measured by cutting withthe restriction enzyme when the transfectants were selected on 6-TG.

Next, integration of a GFP transgene into the HPRT locus wasaccomplished in K562 cells using a similar experimental scheme. In thisexperiment, two donor concentrations were used, where the donor eitherhad short (359 nucleotides) or long (725 nucleotides) regions ofhomology flanking the HPRT insertion site.

The percent integration of the transgene was determined using thesemi-quantitative PCR assay as follows. Three primers (FIG. 5B) thateither amplified a product that was specific for the targetedintegration of the transgene (primers 15512f+ pgkr1) or a product thatwas specific for the wild type HPRT locus lacking the insertion (primers15512f+r1-16078) were used and the ratio of the two PCR productsdetermined. The sequences of the primers used were:

15512f: 5′ AGCCACTGGCCCAGTTTCTACAGTCTC 3′ (SEQ ID NO: 58) pgkr1: 5′GACGTGCGGCTTCCGTTTGTC 3′ (SEQ ID NO: 59) r1-16078: 5′GCCTCCCATCTCCTTCATCACAT 3′ (SEQ ID NO: 60)

As shown in FIG. 5, and as with the insertion of the restriction sitedescribed above, integration of the GFP transgene donor was alsoenriched 2-3 fold by 6-TG selection as measured in the semi-quantitativePCR based assay. The PCR product indicative of transgene integration isshown by the arrow in FIG. 5A. Up to 26% insertion of the transgene intothe HPRT locus was detected, with a 2-3 fold enrichment on targetedintegration upon 6-TG selection.

Example 5 Use of 6-TG Selection for Gene Correction of Human Beta Globin

We then tested modification of the human beta-globin locus by a targetedintegration donor after co-transfection with beta-globin targeted ZFNs,HPRT ZFNs and selection using 6-TG. In this experiment, cells weretransfected with HPRT ZFNs and with the beta globin-specific ZFNs shownin Table 3 below:

TABLE 3 Human beta globin specific zinc finger nucleases SBS #, DesignTarget F1 F2 F3 F4 F5 SBS DRSNLSR QSGDLTR RSDTLSQ QSGSLTR QNATRIK #26755 (SEQ ID (SEQ ID (SEQ ID (SEQ ID (SEQ ID ggGCAGTAA NO: 19) NO: 49)NO: 10) NO: 33) NO: 50) CGGCAGACt tctcctcag g (SEQ ID NO: 47) SBSRSDSLSR DSSNRKT RSAALSR RLDNRTA RSSHLSR # 26758 (SEQ ID (SEQ ID (SEQ ID(SEQ ID (SEQ ID tgGGGcAAG NO: 51) NO: 52) NO: 53) NO: 54) NO: 55)GTGAACGTG gatgaagtt g_ (SEQ ID NO: 48)

The donor comprised ˜1.1 kb of homology of the beta-globin gene flankingthe sickle mutation into which a HhaI restriction site was introduced.Two concentrations of the 29251/29250 HPRT-specific ZFNs were used, low(20 ng of each ZFN per reaction) and high (80 ng of each ZFN). Followingrecovery from transfection, the cells were split and half were subjectto 6-TG selection. At completion of selection, DNA was isolated and thetargeted region around the beta globin was PCR amplified. For thisexperiment, the following primers were used:

Betaglobin F: (SEQ ID NO: 56) CCAGAAGGTTTTAATCCAAATAAGGAGAAGATATGBetaglobin R: (SEQ ID NO: 57) AACGATCCTGAGACTTCCACACTGATGC

The PCR product contains the HhaI restriction site, and followingamplification of the targeted beta globin locus, cleavage of the PCRproduct with the HhaI restriction enzyme produces two fragments if thedonor integration has occurred. As shown in FIG. 6, a dramatic increasein gene correction frequency at the beta globin locus in the 6-TGselected cells was observed, indicating cleavage with HhaI occurred anddemonstrating that selection on 6-TG can result in a cell pool thatcontained 67% gene correction.

Example 6 Modification of HPRT in Human CD34 Cells

HPRT ZFN expression plasmids were transfected into peripheral bloodmobilized hematopoietic stem cells (CD34+ cells from a male donor, i.e.these cells only had one copy of the HPRT gene per cell). Briefly,200,000 cells were transfected by Amaxa nucleofection as described inPerez, ibid. In this experiment, two sets of HPRT specific ZFNs wereused, either the 29251/29250 pair or the 30179/29250 pair at twoconcentrations, either 200 (+) or 400 (++) ng of each ZFN expressionplasmid per nucleofection. Following recovery from the transfection,cells were split into pools and grown in the presence or absence of6-TG. After selection was complete, modification at the HPRT locus wasanalyzed by the Cel-I mismatch assay as described in Example 3.

As shown in FIG. 7, in the presence of the 6-TG selection, up to 84% ofthe amplified DNA showed modification at the HPRT locus. The frequencyof modification of the HPRT locus in the various samples is listed beloweach lane. “C” indicates a control nucleofection with a GFP encodingplasmid.

Example 7 Modification of HPRT Using TALENs

TALENs specific for HPRT were also tested in K562 cells. For theseexperiments, ten different TALENs were constructed wherein the FokIdomain was attached to a +63 C-terminal TALE variant (see U.S. patentapplication Ser. No. 13/068,735). The target nucleotide and RVDs usedfor each position are shown below in Table 4. In the table, the targetnucleotides for the RO and half repeats are shown at each side of thetarget sequence and the identities of each RVD in each repeat unit(second row in each set) are shown below the identity of each targetnucleotide (first row in each set) (SEQ ID NOs:69-78). The TALENsconstructed range from 11-16 full repeats, thus in Table 4, the TALENsthat have less than 16 repeats have (N/A) in positions 15, 14, 13, or 12as is necessary.

TABLE 4 Target and RVDs for HPRT-specific TALENs (Table 4 discloses SEQID NOS 69-78, respectively, in order of appearance) 5′--- targetsequence--- 3′ Half SBS# R0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16Repeat 101288 5′ t G G A T C T A T C A C T A T T ^((N/A)) T 3′ NN NN NING HD NG NI NG HD NI HD NG NI NG NG ^((N/A)) NG 101270 5′ t G C T C A CC A C G A ^((N/A)) ^((N/A)) ^((N/A)) ^((N/A)) ^((N/A)) C 3′ NN HD NG HDNI HD HD NI HD NN NI ^((N/A)) ^((N/A)) ^((N/A)) ^((N/A)) ^((N/A)) HD101267 5′ t C C G T T A T G G C G A ^((N/A)) ^((N/A)) ^((N/A)) ^((N/A))C 3′ HD HD NN NG NG NI NG NN NN HD NN NI ^((N/A)) ^((N/A)) ^((N/A))^((N/A)) HD 101272 5′ t G G G C C T G A A C C G G C ^((N/A)) ^((N/A)) C3′ NN NN NN HD HD NG NN NI NI HD HD NN NN HD ^((N/A)) ^((N/A)) HD 1012715′ t G G C G T C G T G G T G A G ^((N/A)) ^((N/A)) C 3′ NN NN HD NN NGHD NN NG NN NN NG NN NI NN ^((N/A)) ^((N/A)) HD 101286 5′ t C T A T C AC T A T T T C T A ^((N/A)) T 3′ HD NG NI NG HD NI HD NG NI NG NG NG HDNG NI ^((N/A)) NG 101284 5′ t T G C T G A C C T G C T G G A T T 3′ NG NNHD NG NN NI HD HD NG NN HD NG NN NN NI NG NG 101282 5′ t T T G C T G A CC T G C T G G A T 3′ NG NG NN HD NG NN NI HD HD NG NN HD NG NN NN NI NG101276 5′ t G T A G G A C T G A A C G T C T T 3′ NN NG NI NN NN NI HD NGNN NI NI HD NN NG HD NG NG 10 5′ t G G C C T C C C A T C T C C ^((N/A))^((N/A)) T 3′ NN NN HD HD NG HD HD HD NI NG HD NG HD HD ^((N/A))^((N/A)) NG

The TALEN pairs were introduced into K562 cells and 3 or 11 daysfollowing introduction, DNA was isolated from the cells, the regionsurrounding the HPRT locus PCR amplified, and then subjected to theCel-I mismatch assay as above.

As shown in FIG. 8 and Table 5, TALENs modified the HPRT locus. FIG. 8Adepicts the gel from the Cel-I mismatch assay on the day 11 samples, andFIG. 8B shows the percent of modification at the HPRT locus at day 11.Triangles over the lanes in FIG. 8A indicate the increasingconcentration of TALEN expression vector in each grouping (see, Table 5below). The lanes identities are shown below in Table 5 where ‘DNAconc.’ indicates the amount of expression plasmid that was used in eachcondition and both the modification or “% NHEJ” results for both day 3and day 11 are given.

TABLE 5 Lane contents and experimental details day 11 day 3 LaneZFN/TALEN Pair DNA conc. % NHEJ % NHEJ 1 101270:101267 400 ng 5.2% 4.5%2 800 ng 9.9% 12.5% 3 1600 ng  26.2% 31.8% 4 101272:101271 400 ng 2.3%3.4% 5 800 ng 5.4% 7.6% 6 1600 ng  17.0% 19.1% + 101270:101267 800 ng15.3% N/A G GFP 400 ng 0.0% 0.0% 7 101278:101276 400 ng 0.7% 1.7 8 800ng 2.7% 10.1 9 1600 ng  25.4% 35.3 10 101286:101284 400 ng 5.4% 25.6 11800 ng 13.8% 28.4 12 1600 ng  13.6% 35.3 13 101288:101282 400 ng 11.1%17.7 14 800 ng 26.1% 33.4 15 1600 ng  29.7% 46.2 16 101288:101284 400 ng10.9% 24.8 17 800 ng 22.0% 34.6 18 1600 ng  39.5% 62.2 19 ZFN 29250/51400 ng 20.6% 30.4 20 800 ng 41.3% 69.2 21 1600 ng  18.6% 38.8 +101288:101282 800 ng 26.9% G GFP 400 ng 0.0% 0.0

Thus, HPRT-specific TALENs are capable of efficiently cleaving the HPRTlocus.

Example 8 Cleavage of Canine HPRT

The HPRT1 specific nuclease pairs were then tested in canine cells invitro. In these experiments, the lead human HPRT1 ZFN and TALEN nucleasepairs were used, and the alignment of the human and canine (dog)sequences surrounding the nuclease targets sites is shown in FIG. 9.Inspection of the alignment of the human and canine sequences revealssimilarity at the target sites. Thus, the nuclease pairs weretransfected into the dog cell line D17 by nucleofection of variousamounts of the corresponding nuclease expression vectors. The pairstested and quantities of DNA used in the nucleofection are shown belowin Table 6 where the lanes correspond to FIG. 10:

TABLE 6 Cleavage of canine HPRT Lane nuclease pair Conc. of DNA (ng) %NHEJ 1 29251:29250 100 0.0 2 30179:29250 100 9.2 3 29223:29216 100 0.0 4101284:101288 100 25.1 5 101276:101278 100 0.0 6 GFP (control) 100 0.0 729251:29250 200 2.8 8 30179:29250 200 4.7 9 29223:29216 200 0.0 10101284:101288 200 16.2 11 101276:101278 200 2.5 12 GFP (control) 200 0.013 29251:29250 400 0.0 14 30179:29250 400 0.0 15 29223:29216 400 0.0 16101284:101288 400 14.3 17 101276:101278 400 0.0 18 GFP (control) 400 0.019 Mock (control) — 0.0

Analysis of gene modification levels with a PCR primer pair specific forthe dog HPRT locus followed by Cel-I mismatch assay showed that somenuclease pairs modified the dog HPRT locus very efficiently (see FIG. 10and Table 6). The efficiency of gene modification of the variousnuclease pairs correlates well with the degree of conservation of therespective binding sites between the human and dog HPRT genes.

Example 9 Cleavage of Rhesus HPRT

The binding sites of the lead human specific ZFN and TALEN HPRT pairsare conserved between human and the rhesus monkey. Therefore, we testedthese nucleases against the rhesus cell line LLC-MK2, and found asexpected, that the nucleases demonstrated efficient cleavage.

The nuclease pairs used and percent modification observed of HPRT asdetermined by the Cel-I mismatch assay, are shown below in Table 7 andthe gel analysis is shown in FIG. 11.

TABLE 7 Modification of rhesus monkey HPRT Lane nuclease pair % NHEJ 129251:29250 8.2 2 30179:29250 0.0 3 29233:29216 2.7 4 101284:101288 8.75 101276:101278 7.6 6 GFP 0.0

These data demonstrate that the human-specific nucleases that modify theHPRT locus are also capable of modifying the rhesus monkey HPRT gene.

Example 10 Cleavage of Human HPRT Introns

ZFN pairs shown below in Table 8 were transfected as mRNA into eitherCD34+ cells (pairs A-F) or into K562 cells (pair A′) via BTX®transfection according to manufacturer's protocol. For eachtransfection, 250,000 cells were used. DNA was harvested by standardprocedures on day 3 post-transfection.

FIG. 12 shows the activity of the seven nuclease pairs with thepercentage modification as assayed by the Cel I assay. Thus the ZFNpairs cleaved the HPRT intronic DNA. The oligonucleotides used for PCRfor CEL-I analysis are shown below.

TABLE 8 Intronic HPRT ZFN pairs Site ZFN pair CEL-I primer, FCEL-I primer, R A 34270:34269 TGT CCT TGG CCA CAC TGT TAGGG AGT AAA ATG ACA TGG CCT A (SEQ ID NO: 151) (SEQ ID NO: 152) B34278:34277 ATG CCT TTT GGG AAG AGT TG CCA GCC AGA ACT CCT TGA AA(SEQ ID NO: 153) (SEQ ID NO: 154) C 34306:34303CTG GCA TAA TCT TTT CCC CC TTT GAG GTT TCC AGT GCT GA (SEQ ID NO: 155)(SEQ ID NO: 156) D 34321:35944 TCA GCA CTG GAA ACC TCA AACCA CGC CTG GTC ACT TTC (SEQ ID NO: 157) (SEQ ID NO: 158) E 35974:35963CTC CTT GGC TGA GAG GAG TG TTA ACT CTC TTG CCT GGC CT (SEQ ID NO: 159)(SEQ ID NO: 160) F 34359:35981 CTT GGG GCA AAC AGG AGT ATAAA GAA AGA AAA GGC AAC AAG C (SEQ ID NO: 161) (SEQ ID NO: 162) A′37714:37706 CTT GGG GCA AAC AGG AGT AT AAA GAA AGA AAA GGC AAC AAG C(SEQ ID NO: 163) (SEQ ID NO: 164)

Example 11 Targeted Integration into the Human HPRT Locus in CD34+ Cells

In FIG. 13, an oligonucleotide donor was co-transfected with theindicated ZFN mRNA pairs. PCR products were generated using theoligonucleotides shown in Table 8. Integration of the exogenous DNAsequence into the HPRT intron was assayed by digestion with therestriction enzyme indicated below. We thus demonstrated modification ofthe human HPRT locus in CD34+ cells. The DNA sequence of theoligonucleotide donors and the restriction enzymes used for detection oftargeted integration are shown in Table 9 below. Asterisks indicatephosphorothioate linkages.

TABLE 9 Oligonucleotide donor sequences Restriction Site enzymeOligonucleotide donor sequence A KpnIC*A *CT GTG ACC TGC ATA CTA CAA GTC TAC TTT GTT TTC TAT CCATTG TTT GTA TCT GGG TAC CTT GCA AAA GGT AGG AAA AGG ACC AACCAG ATC AGC AGA GAA GAG TTG CCT TGG AGT TTT *C* T (SEQ ID NO: 137) AKpnI A*G *AA AAC TCC AAG GCA ACT CTT CTC TGC TGA TCT GGT TGG TCCTTT TCC TAC CTT TTG CAA GGT ACC CAG ATA CAA ACA ATG GAT AGAAAA CAA AGT AGA CTT GTA GTA TGC AGG TCA CAG *T* G (SEQ ID NO: 138) BSphI G*C *CA GAA TTC CTG TTT TAG AAT ACA TCT CTG CTG ATC TGT CTGTAT TCT TAG ACT GCA TGC ATC TGG GAT GAA CTC TGG GCA GAA TTCACA TGG GCT TCC TTT GAA ATA AAC AAG ACT TTT *C* A (SEQ ID NO: 139) BSphI T*G *AA AAG TCT TGT TTA TTT CAA AGG AAG CCC ATG TGA ATT CTGCCC AGA GTT CAT CCC AGA TGC ATG CAG TCT AAG AAT ACA GAC AGATCA GCA GAG ATG TAT TCT AAA ACA GGA ATT CTG *G* C (SEQ ID NO: 140) CNcoI G*A *CC AGG GGC ATG TCC TGG TCC ACC TAC CTG AAA ATG TTT GCAACC AGC CTC CTG GCC ATG GTT GCA CAG GGG CTG AAG TTG TCC CACAGG TAT TAC GGG CCA ACC TGA CAA TAC ATG AAG *T* T (SEQ ID NO: 141) CNcoI A*A *CT TCA TGT ATT GTC AGG TTG GCC CGT AAT ACC TGT GGG ACAACT TCA GCC CCT GTG CAA CCA TGG CCA GGA GGC TGG TTG CAA ACATTT TCA GGT AGG TGG ACC AGG ACA TGC CCC TGG *T* C (SEQ ID NO: 142) DClaI T*T *AA TTA TGG TTT GAC CAA TAT TTA TTG GAA ACC GCC AAA GCTTAA ATC ATC AGC TAT CGA TGA ATG TGA TTT GAA AGG TAA TTT AGTATT GAA TAG CAT GTG AGC TAG AGT ATT TCA T*T *C (SEQ ID NO: 143) D ClaIG*A *AT GAA ATA CTC TAG CTC ACA TGC TAT TCA ATA CTA AAT TACCTT TCA AAT CAC ATT CAT CGA TAG CTG ATG ATT TAA GCT TTG GCGGTT TCC AAT AAA TAT TGG TCA AAC CAT AAT T*A *A (SEQ ID NO: 144) E PvuIIG*T *GG GAA GCT TGT TCC AGA CAG CCA AGG AGG GAG GTT CGC GCAGTT CCT TTG GCC ACC CAG CTG TGG GGT AAT TGA TCC ATG TAT GCCATT CAT GTA CAA TGT AGG CAC TTA TAC CTG TAT *T* C (SEQ ID NO: 145) EPvuII G*A *AT ACA GGT ATA AGT GCC TAC ATT GTA CAT GAA TGG CAT ACATGG ATC AAT TAC CCC ACA GCT GGG TGG CCA AAG GAA CTG CGC GAACCT CCC TCC TTG GCT GTC TGG AAC AAG CTT CCC *A* C (SEQ ID NO: 146) FHindIII G*A *CT CCA TAC TTT TCA GTT CTT GAA TAT TTT TTC CTT TAT TCC TCTTGT CTC TGT AAA GCT TAC ATC AAC TGG AGT TGG ACT GTA ATA CCAGGT ATC TCC AGA AGA TGG CAC TAT TTA ACA G*A *T (SEQ ID NO: 147) FHindIII A*T *CT GTT AAA TAG TGC CAT CTT CTG GAG ATA CCT GGT ATT ACAGTC CAA CTC CAG TTG ATG TAA GCT TTA CAG AGA CAA GAG GAA TAAAGG AAA AAA TAT TCA AGA ACT GAA AAG TAT GGA G*T *C (SEQ ID NO: 148)

Example 12 Targeted Integration of a Transgene into the Human HPRT Locusin K562 Cells

Plasmid DNA donors were constructed containing 476 bp of HPRT DNAflanking the site C cleavage site on the 5′ and 354 bp of HPRT DNAflanking the cleavage site on the 3′. In between these regions ofchromosomal homology was placed a strong splice acceptor sequence(DeKelver et al. (2010) Genome Research 20:1133-1142). Similarly, donorswere constructed containing 429 bp of HPRT homology on the 5′ end, and616 bp of HPRT homology on the 3′ end for the site A cleavage site.Next, in frame with HPRT was placed DNA sequence encoding the viral 2Aself cleavage peptide followed by the gene for the green fluorescentprotein. The polyadenylation signal from the bovine growth hormone genewas inserted after the transgene coding sequence. This plasmid wasco-transfected into K562 cells with mRNA encoding the site C or site AZFN pair. Cultures were split in half four days post-transfection and6-TG selection applied to one half of the cells as described above.Culture viability and the percentage of GFP-positive cells were assayedone week after 6-TG selection by Guava-based cell fluorescencemeasurement according to manufacturer's protocol. The resultsdemonstrate successful integration of the transgene into HPRT and thesuccessful selection of HPRT-negative, transgene-containing cells with6-TG.

Next, the targeted integration into site C was assayed by PCR (FIG. 15).Two systems of donor deliver were tested: delivery from a plasmid (P) asdescribed above, or delivery using a plasmid further containing AAV2ITRs (A). The HPRT locus was amplified by PCR using the oligonucleotides5′-AGT ACT CTG GAT CTT CCT GAT T-3′ (SEQ ID NO:149) and 5′-CCC ATT CACCAT TAT ATT CAA AGT C-3′ (SEQ ID NO:150). The wild-type HPRT gene givesa 968 bp PCR product; an HPRT allele with the transgene inserted gives a2076 bp PCR product.

Example 13 Targeted Integration of a Transgene into the Human HPRT Locusin CD34+ Cells

Next, the transgene donor for site C was integrated into HPRT in CD34+cells. Cells were transfected with the site C ZFNs via Amaxanucleofection of the encoding mRNAs according to manufacturer's protocoland donor was delivered via the AAV2 plasmid described above.

As shown in FIG. 16, The number of GFP-positive cells assayed three dayslater by Guava according to manufacturer's protocols and demonstratedsuccessful targeted integration into CD34+ cells.

All patents, patent applications and publications mentioned herein arehereby incorporated by reference in their entirety.

Although disclosure has been provided in some detail by way ofillustration and example for the purposes of clarity of understanding,it will be apparent to those skilled in the art that various changes andmodifications can be practiced without departing from the spirit orscope of the disclosure. Accordingly, the foregoing descriptions andexamples should not be construed as limiting.

What is claimed is:
 1. A non-naturally occurring fusion proteincomprising a transcription activator like effector domain DNA bindingprotein (TALE) that binds to a target site in an endogenous hypoxanthineguanine phosphoribosyltransferase (HPRT) gene comprising a nucleotidesequence selected from the group consisting of SEQ ID NOs:69-78 and anuclease cleavage domain, wherein the TALE domain comprises a repeatvariable diresidue (RVD) sequence in the order presented and selectedfrom a single row of Table
 4. 2. A polynucleotide encoding thenon-naturally occurring fusion proteins of claim
 1. 3. An isolated cellcomprising the fusion proteins of claim
 1. 4. An isolated cellcomprising the polynucleotides of claim
 2. 5. The isolated cell of claim3, wherein the cell is selected from the group consisting of a T-cell, aB-cell or a stem cell.
 6. The isolated cell of claim 5, wherein the stemcell is selected from the group consisting of an embryonic stem cell(ESC), an induced pluripotent stem cell (iPSC), a CD34+ hematopoieticstem cell and a hepatic stem cell.
 7. The isolated cell of claim 4,wherein the cell is selected from the group consisting of a T-cell, aB-cell, or a stem cell.
 8. The isolated cell of claim 7, wherein thestem cell is selected from the group consisting of an embryonic stemcell (ESC), an induced pluripotent stem cell (iPSC), a CD34+hematopoietic stem cell, and a hepatic stem cell.
 9. A kit comprisingthe fusion protein of claim
 1. 10. A kit comprising the polynucleotideof claim
 2. 11. A method of cleaving an endogenous HPRT gene in anisolated cell, the method comprising: transforming or transfecting saidisolated cell comprising said HRPT gene with the polynucleotide of claim2, culturing said transformed or transfected isolated cell underconditions such that said fusion proteins is expressed and the HPRT geneis cleaved.
 12. The method of claim 11, wherein the cell is selectedfrom the group consisting of a T-cell, a B-cell or a stem cell.
 13. Themethod of claim 12, wherein the stem cell is selected from the groupconsisting of an embryonic stem cell (ESC), an induced pluripotent stemcell (iPSC), a CD34+ hematopoietic stem cell, and a hepatic stem cell.14. A method of enriching for cells modified by a nuclease at anendogenous HPRT locus, the method comprising: cleaving said endogenousHPRT gene in said isolated cell according to the method of claim 11;introducing into the cell, said polynucleotide encoding said fusionprotein for modification of a second locus of the endogenous HPRT gene;subjecting the cells to selection with 6-thioguanine, thereby enrichingthe cells for those in which the endogenous locus has been modified. 15.The method of claim 14, wherein the endogenous locus is inactivated. 16.The method of claim 14, wherein the isolated cell is selected from thegroup consisting of a T-cell, a B-cell or a stem cell.
 17. The method ofclaim 16, wherein the stem cell is selected from the group consisting ofan embryonic stem cell (ESC), an induced pluripotent stem cell (iPSC), aCD34+ hematopoietic stem cell and a hepatic stem cell.